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Constitutive activation of Jak-2 and Tyk-2 in a v-Src-transformed human gallbladder adenocarcinoma cell line
1Department of Human Genetics, National Institute of Genetics, Shizuoka, Japan.
Abstract:
It is well known that v-Src phosphorylates various substrates on tyrosine residue and associates with tyrosine-phosphorylated proteins as well as proline-rich ligands through its SH2 and SH3 domains, respectively, thereby inducing oncogenic transformation. A signal pathway from the cell surface to genes in the nucleus, the Jak/STAT (signal transducers and activators of transcription) pathway, has been shown to be involved in the signal transduction mechanism mediated by many cytokines and growth factors. Although a member of the STAT family, STAT3 has been reported to be constitutively activated in several v-Src-transformed cells, and it still remains unknown whether Jak molecules, which act upstream of STATs, are involved in the v-Src-induced activation mechanism of STAT3. In this study, we analyzed activations of both Jak and STAT molecules using v-Src-transformed HAG-1 cells derived from a human gallbladder adenocarcinoma. STAT3 was found to be constitutively activated in v-Src-transformed HAG-1 cells, but not in either non-transformed mock-transfected or activated c-H-ras-transfected HAG-1 cells, even though the other known STAT molecules are expressed. Furthermore, both Jak-2 and Tyk-2 were constitutively activated only in v-Src-transformed HAG-1 cells. Association of v-Src with either STAT3 or the Jak molecules was not observed. No change of this activation was detected by either interferon (IFN)-alpha2a or IFN-gamma, which had shown inhibitory effects on the growth of v-Src-transformed HAG-1 cells. These results raise the possibility that Jak-2 and Tyk-2 are both activated by v-Src, thereby contributing to the constitutive activation of STAT3 in the v-Src-transformed cells.
Insights
v-Src oncogene activates Janus kinase-2 (Jak-2) and Tyrosine kinase-2 (Tyk-2), leading to constitutive activation of Signal transducer and activator of transcription 3 (STAT3) in human gallbladder adenocarcinoma cells.
Area of Science:
- Oncology
- Molecular Biology
- Signal Transduction
Background:
- v-Src is known to induce oncogenic transformation by phosphorylating substrates and interacting with specific protein domains.
- The Janus kinase/Signal transducer and activator of transcription (Jak/STAT) pathway is crucial for signal transduction initiated by cytokines and growth factors.
- Constitutive activation of STAT3 has been observed in v-Src-transformed cells, but the upstream involvement of Jak molecules remains unclear.
Purpose of the Study:
- To investigate the role of Jak molecules in v-Src-induced STAT3 activation.
- To analyze the activation status of Jak and STAT molecules in v-Src-transformed human gallbladder adenocarcinoma cells (HAG-1).
Main Methods:
- Analysis of Jak and STAT activation in v-Src-transformed HAG-1 cells.
- Comparison with non-transformed and c-H-ras-transfected HAG-1 cells.
- Assessment of v-Src association with STAT3 and Jak molecules.
- Evaluation of interferon (IFN) effects on activation.
Main Results:
- STAT3 was constitutively activated in v-Src-transformed HAG-1 cells, but not in control cells.
- Both Jak-2 and Tyk-2 were constitutively activated exclusively in v-Src-transformed HAG-1 cells.
- No direct association was found between v-Src and STAT3 or Jak molecules.
- Interferons (IFN-alpha2a and IFN-gamma) did not alter this activation pattern.
Conclusions:
- v-Src likely activates Jak-2 and Tyk-2.
- This activation of Jak-2 and Tyk-2 contributes to the constitutive activation of STAT3 in v-Src-transformed cells.
- The findings suggest a novel mechanism of STAT3 activation mediated by v-Src via Jak kinases.