Down-regulation of JAK1 by RNA interference inhibits growth of the lung cancer cell line A549 and interferes with the PI3K/mTOR pathway.

PURPOSE: The mammalian Janus kinase (JAK) family plays a critical role in cytokine/growth factor signalling pathways and is associated with human cancers. In this study, we explored the role of JAK1 in the non-small cell lung cancer (NSCLC) cell line A549 and its molecular crosstalk with the phosphatidyl inositol-3-kinase (PI3K)/mammalian target of the rapamycin (mTOR) pathway.
METHODS: One hundred and two NSCLC and 50 normal lung specimens were collected after surgical resection. JAK1 expression and phosphorylation were determined via immunohistochemical staining (IHC) assay. A stable knockdown of JAK1 was performed in A549 cells by RNA interference. Stable cell proliferation, cell cycle, apoptosis, and invasion were characterised in vitro. Tumourigenicity was analysed in vivo. The NSCLC xenograft protein expression of PI3K/mTOR pathway molecules was determined by Western blot assay.
RESULTS: JAK1 expression was higher in NSCLC tissues than in normal lung tissues (P < 0.01). JAK1 knockdown in A549 cells significantly inhibited cell proliferation and invasion while promoting cell arrest at G0/G1 phase (all P < 0.05). The xenograft model showed that JAK1 suppression inhibited tumour growth compared with normal control (P < 0.05). Moreover, JAK1 knockdown inhibited mTOR or P70 ribosomal protein S6 kinase (P70S6K) phosphorylation, but increased glycogen synthase kinase-3α (GSK-3α) and B-cell lymphoma-extra large (Bcl-xl) phosphorylation. Total protein expression and Akt1/2 phosphorylated status remained unchanged.
CONCLUSION: Our study suggests that JAK1 expression and phosphorylation is abnormal in NSCLC tissues. The knockdown of JAK1 significantly inhibits tumourigenicity of the A549 cell line and demonstrates that crosstalk between the JAK1 and PI3K/mTOR pathways is involved.