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Human Cancer Biology |
Authors' Affiliations: Departments of 1 Pathology, 2 Internal Medicine, and 3 Microbiology, College of Medicine, The Catholic University of Korea, Seoul, Korea
Requests for reprints: Sug Hyung Lee, Department of Pathology, College of Medicine, The Catholic University of Korea, 505 Banpo-dong, Socho-gu, Seoul 137-701, Korea. Phone: 82-2-590-1188; Fax: 82-2-537-6586; E-mail: suhulee{at}catholic.ac.kr.
| Abstract |
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Experimental Design: We analyzed 494 tissues from 186 acute adulthood leukemias, 30 multiple myelomas, and 278 common solid cancers, including 90 breast, 47 gastric, 47 colon, 47 lung, and 47 hepatocellular carcinomas by single-strand conformation polymorphism analysis.
Results: Overall, we found six JAK1 mutations (four in acute leukemias, one in a lung carcinoma, and one in a breast carcinoma) and three JAK3 mutations (two in breast carcinomas and one in a gastric carcinoma). Of note, three JAK1 mutations were an identical p.V658F mutation, which is homologous to JAK2 p.V617F mutation. We also found two other JAK1 mutations that occurred at very close sites (p.T782M and p.L783F). We found three of the four leukemias with JAK1 mutations expressed mutated JAK1 at the mRNA level. For JAK3 mutations, one of them was JAK3 p.V715I that is homologous to the JAK1 p.L783F. These recurrent mutations in identical and homologous sites suggest a possibility that alterations of these amino acids might be important for tumor pathogenesis. With respect to the cancer types, T-acute lymphoblastic leukemia (T-ALL) showed the highest incidence of the mutations (3 of 11; 27.3%).
Conclusion: Our data indicate that both JAK1 and JAK3 mutations occur in common human cancers and that JAK1 mutation in T-ALL is a frequent event. The data suggest that some of the JAK1 and JAK3 mutations may to be functional and contributes to cancer development, especially to T-ALL development.
Activation of JAKs is implicated in tumorigenesis, and genetic alterations of genes encoding JAKs are partly responsible for activations of JAK signaling (3). A chromosomal translocation results in fusion of JAK2 and TEL to generate TEL-JAK2 kinase, which is detected in some patients with leukemias (4). Recently, a missense somatic mutation in JAK homology 2 pseudokinase domain of JAK2 gene (JAK2 p.V617F) has been reported in chronic myeloproliferative disorders (5, 6). The mutation was observed in most polycythemia vera as well as in about one third of both essential thrombocythemia and myeloid metaplasia with myelofibrosis. Functionally, this mutation constitutively activates JAK2 signaling, suggesting its role in the neoplastic transformation (5, 6). In addition to the JAK2 mutations, JAK3 mutations were also detected in acute megakaryoblastic leukemia (p.A572V, p.V722I, and p.P132T), and these mutations were activating mutations that confer growth factor-independent growth on cells (7). These data indicate that not only JAK2 but also other JAK genes are mutated in human cancers, and suggest a possibility that JAK genes might be targets for somatic mutations in human cancers. Because activation of JAK signaling frequently occurs in human cancers (3, 8), it is also necessary to identify whether the activation is originated from somatic mutations of JAK genes.
Recently, research groups in the United States and the United Kingdom screened all of the kinase genes for the detection of somatic mutations in several cancer types and found that somatic mutations of JAK1, JAK3, and TYK2 genes are rare in the cancers (9, 10). However, following questions about JAK gene mutations in cancers remain unanswered: (a) whether other types of human cancers besides the ones analyzed in the previous studies have JAK mutations; and (b) whether there is any ethnic difference of the mutations. In this study, we investigated presence of JAK1, JAK3, and TYK2 mutations in acute adulthood leukemias and common solid cancers (breast, colorectal, lung, gastric, and hepatocellular carcinomas) by a PCR-single strand conformation polymorphism (SSCP) assay.
| Materials and Methods |
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SSCP analysis and DNA sequencing. For the solid cancers, malignant cells and normal cells were selectively procured from H&E-stained slides using a 301/2 gauge hypodermic needle affixed to a micromanipulator, as described previously (12). In this study, primary lesions, but not the metastatic lesions, were analyzed for the mutation detection. DNA extraction was done by a modified single-step DNA extraction method (12). For the leukemias, we extracted DNA from nonfixed fresh bone marrows of the patients. To date, JAK2 p.V617F (exon 12), JAK3 p.P132T (exon 4), JAK3 p.A572V (exon 13), and JAK3 p.V722I (exon 16) mutations have been detected in human cancers (7, 9, and 10). Thus, we focused our mutational analyses on the corresponding exons of JAK1, JAK3, and TYK2 genes (JAK1 exons 5, 14, and 17; JAK3 exons 4, 13, and 16; TYK2 exons 14 and 17). Genomic DNA each from cancer cells and normal cells were amplified by PCR with primer pairs (Table 1 ). Radioisotope was incorporated into the PCR products for detection by autoradiogram. After SSCP, DNAs showing mobility shifts were cut out from the dried gel and reamplified for 30 cycles using the same primer sets. Sequencing of the PCR products was carried out using the cyclic sequencing kit (Perkin-Elmer). The procedures of PCR and SSCP analysis were done as described previously (12). We previously analyzed JAK2 V617F mutation in the same cancer tissues, and the data were compared in this study (13).
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Reverse transcription-PCR. To see whether mutated JAKs are expressed in the cancers, we analyzed mRNA expression of the mutated JAKs by reverse transcription-PCR. Total RNA was extracted from fresh bone marrow aspirates using TRIzolLS reagent following the manufacturer's protocol (Life Technology). Reverse transcription and subsequent PCR were done using a polymerase in a single step without changing reaction mixtures (SuperScript III One-Step RT-PCR system; Invitrogen). To detect the JAK1 c.1972G>T (p.V658F) mutation, a forward primer (5'-GTCTTAGACCCCAGCCACAG-3') and a reverse primer (5'-CCCCTTCCACAAACTCTTCC-3') were used for the RT-PCR. To detect the JAK1 c.2347C>T (p.L783F) mutation, a forward primer (5'-CCCATTACGGTGCTGTC-3') and a reverse primer (5'-CCGGCTTTCATAGAATCTCT-3') were used. The PCR products were run on agarose gels, and the corresponding bands were cut out from the gel. Sequencing of the PCR products was carried out using a capillary automatic sequencer (ABI Prism Genetic Analyzer; Applied Biosystem) according to the manufacturer's recommendation.
| Results |
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2 test).
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To see whether the sequence variants detected in this study are indeed somatic mutations confined to the cancers or polymorphisms in the population, we analyzed the altered DNA sequences in normal tissues from 100 healthy persons. However, we did not find the same sequence variants in the samples. Also, the SSCPs from the cancer DNA showed mobility shifts, whereas the SSCP from the corresponding normal DNA from the same patients did not show any mobility shift (Figs. 1 and 2). Because polymorphisms should be detected in both normal and cancer cells, we concluded that the detected sequence variations in this study are somatic mutations, not polymorphisms.
To see the expression of the mutant JAK1, we analyzed mRNA expression of JAK1 in four leukemias with the JAK1 mutations (acute leukemia #104, #120, #136, and #182). For the c.1972G>T (p.V658F) mutant, two (#136 and #182) of the three leukemias strongly expressed JAK1 mRNA (Fig. 3A ). For the c.2347C>T (p.L783F) mutant, the leukemia with the mutation (#120) strongly expressed JAK1 mRNA (Fig. 3A). By DNA sequencing, we found the RT-PCR products (#120, #136, and #182) represented mutated JAK1 as well as wild-type JAK1 (Fig. 3B and C). As for the gastric, breast, and lung cancers with JAK1 or JAK3 mutations, we could not analyze mRNA expression, because the tissues for RT-PCR were not available.
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| Discussion |
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The JAK1 p.V658F mutation is homologous to the JAK2 p.V617F mutation (National Center for Biotechnology Information database), which constitutively activates JAK2 signaling (5). Recently, Staerk et al. (15) showed that JAK1 p.V658F mutation led to constitutive activation of JAK1. The JAK2 p.V617F mutant may activate JAK2 by relieving the inhibition of JAK homology 1 domain by the JAK homology 2 domain where p.V618F resides. We hypothesize that JAK1 p.V658F mutant may activate JAK1 signaling similarly and contribute to tumorigenesis in vivo. We found JAK1 mutations p.T782M and p.L783F. Interestingly, the corresponding residue of JAK1 leucine at position 783 is JAK3 valine at 715, a replacement of which was observed in this study (JAK3 p.V715I). A close proximity of these three mutations (JAK1 p.T782M, JAK1 p.L783F, and JAK3 p.V715I) suggests that these residues may be important in JAK function, and that these mutations might be functional in tumorigenesis. Of note, we found that most of the mutated JAK1 were actively expressed in the acute leukemis at mRNA level. However, one of the leukemias with JAK1 p.V658F mutation did not strongly express the mutated JAK1. Epigenetic modifications such as hypermethylation in CpG island contribute to the loss of protein expression. Recent studies showed that up to 5% of human genes can be hypermethylated in their CpG islands in the promoters (16). Whether the expression of JAK1 p.V658F mutation is inactivated by hypermethylation should be further studied. Mutations at consensus donor and acceptor sequences of an intron have been shown to cause cryptic splice site use and exon skipping in various human disease genes (6). The intron +5G of the donor sequences is a conserved sequence (6). Thus, although functional studies have not been done, it could be conceived that the splice-site mutation (JAK3 c.420+5G>A) found in this study might result in abnormal splicing of JAK3 mRNA. In contrast to JAK1 p.V658F mutation, however, other JAK mutations have not been tested for functional consequences. Therefore, whether they are "functional" or "passenger" mutations remains unknown at this stage.
T-ALL is an aggressive malignant disease of T-cell precursors (17). For survival and proliferation of both normal and neoplastic hematopoietic cells, cytokines play crucial roles (3). Interleukin-7 (IL-7) that is implicated in normal T-cell survival and proliferation activates both JAK1 and JAK3 (3). Interleukin-7 also promotes proliferation of T-ALL (18), suggesting its role in pathophysiology of T-ALL. In the present study, we detected two types of JAK1 mutation in the T-ALL. One of them was the JAK1 p.V658F mutation that had been proven to be an activating mutation (15). The other one was JAK1 p.L783F, the function of which has not been known. As in the case with JAK2 p.V617F mutation of polycythemia vera, the T-ALL cells with the JAK1 mutations might possibly proliferate without cytokines such as interleukin-7. Notch 1 mutation is the best-known mutation in T-ALL, which leads to aberrant Notch signaling (14). Our data showed that three of the T-ALLs with JAK1 mutations harbored Notch1 mutation as well. However, their association was statistically insignificant. Possible differences of T-ALL pathogenesis in T-ALLs with Notch1/JAK1 mutations or Notch1 mutation alone, or JAK1 mutation alone or neither remain clarified. We did the mutational analysis with only 11 adult T-ALLs because adult T-ALL is a rare disease and a larger number of T-ALL samples were not available. Despite the small number of the samples, a recurrent and functionally proven mutation (JAK1 p.V658F) suggests that JAK1 mutation in T-ALL may be a "functional" but not a "passenger" mutation.
Under suitable conditions SSCP is capable of detecting >90% of mutations occurring within any sequence, and the sensitivity of PCR-SSCP is generally believed to be high if the amplified fragments are 200 bps or less in size (19). It is possible that some mutational changes may not be detected by SSCP in this study. However, because we have analyzed the samples by SSCP twice and used primers around 200 bp (150-204 bps), it can be thought that the missing of JAKs mutations, if any, would be very rare in this study. Also, we analyzed the JAK1 mutation in 50 of the 186 acute leukemias used in this study by direct sequencing as well as by SSCP, and no additional mutation was detected by the direct sequencing (data not shown), suggesting that the SSCP is a sensitive method in detecting mutations in this study.
There have been large scale mutational studies on kinase-encoding genes in colorectal, lung, breast, gastric, ovarian and renal carcinomas, melanomas, and gliomas (9, 10). They detected somatic mutations of JAK genes in some cancers, including JAK1 p.E886K in a colorectal carcinoma, JAK1 p.N707fs*7 in a gastric carcinoma, JAK2 p.K191Q in an ovarian carcinoma, JAK3 p.L527P in a gastric carcinoma, and TYK2 p.H732R in a colorectal carcinoma. However, the incidences of the JAK mutations were very low (below 5%), and there was no recurrent mutation in them (9, 10). Moreover, these mutations are not overlapped with the JAK mutations detected in our study, indicating somatic mutations of JAK genes might be passenger mutations and rare in common solid cancers. JAK mutations may be specific to rare hematopoietic disorders such as polycythemia vera (JAK2) and T-ALL (JAK1).
In summary, the present study identified novel mutations of JAK1 and JAK3 in T-ALL, AML, gastric cancer, breast cancer, and lung cancer. Although T-ALL harbored frequent JAK1 mutation, other cancers did not harbor frequent mutation of any JAK gene. The most impressive examples of recent cancer therapies target activated kinases by genetic alterations such epidermal growth factor receptor mutation, ERBB2 amplification, and BCR-ABL translocation (20–22). Thus, research will further focus on evaluating kinases as promising molecular targets for cancer treatment. Because most of the JAK1 mutations detected in this study had been proven to be an activating mutation (V658F), this mutation might have a potential utility for the development of antineoplastic drug targeting T-ALL.
| Disclosure of Potential Conflicts of Interest |
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| Footnotes |
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The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
Note: E.G. Jeong and M.S. Kim, contributed equally to this work.
Received 11/ 6/07; revised 2/12/08; accepted 2/17/08.
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