There is relatively little known about expression and activation of p38 mitogen-activated protein kinases (MAPKs) through G protein-linked, seven-transmembrane-spanning (STM) receptors in mammalian smooth muscle. To investigate the role of p38 MAPK in smooth muscle, we cloned and sequenced the p38 MAPK expressed in canine smooth muscles. A full-length clone of the canine p38 MAPK expressed in colonic smooth muscle was obtained by RT-PCR. The deduced amino acid sequence revealed 99% identity to the human p38 MAPK and differed from the human enzyme in only two conservative substitutions. The deduced molecular mass of the canine p38 MAPK is 41.2 kDa, with a calculated isoelectric point of 5.41. Canine p38 MAPK was found to be expressed in colonic, tracheal, and vascular smooth muscles and underwent increased tyrosine phosphorylation in response to motor neurotransmitters, acetylcholine (ACh) and neurokinin A (NKA), in colonic smooth muscle. There was an eightfold increase in p38 MAPK phosphorylation after a 10-min incubation with ACh and a threefold increase with NKA. We also identified a p38 immunoreactive kinase activity isolated from colonic smooth muscle homogenate by Mono Q chromatography. Partially purified p38 MAPK and activated recombinant p38 MAPK (Mpk2) phosphorylated both the known p38 MAPK substrate ATF2, as well as porcine stomach h-caldesmon in vitro. The results suggest that elements of the “stress-response” pathway may be coupled to transcriptional control as well as to cytoskeletal and possibly contractile protein phosphorylation in mammalian smooth muscle.

Insulin-like Growth Factor (IGF)/IGF-1 Receptor (IGF-1R) signaling is known to regulate stem cell pluripotency and differentiation to trigger cell proliferation, organ development, and tissue regeneration during embryonic development. Unbalanced IGF/IGF-1R signaling can promote cancer cell proliferation and activate cancer reprogramming in tumor tissues, especially in the liver. Hepatocellular carcinoma (HCC) is one of the leading causes of cancer-related death, with a high incidence and mortality rate in Asia. Most patients with advanced HCC develop tyrosine kinase inhibitor (TKI)-refractoriness after receiving TKI treatment. Dysregulation of IGF/IGF-1R signaling in HCC may activate expression of cancer stemness that leads to TKI refractoriness and tumor recurrence. In this review, we summarize the evidence for dysregulated IGF/IGF-1R signaling especially in hepatitis B virus (HBV)-associated HCC. The regulation of cancer stemness expression and drug resistance will be highlighted. Current clinical treatments and potential therapies targeting IGF/IGF-1R signaling for the treatment of HCC will be discussed.

The role of a YAP-IGF-1R signaling loop in HCC resistance to sorafenib remains unknown. Method: Sorafenib-resistant cells were generated by treating naïve cells (HepG2215 and Hep3B) with sorafenib. Different cancer cell lines from databases were analyzed through the ONCOMINE web server. BIOSTORM–LIHC patient tissues (46 nonresponders and 21 responders to sorafenib) were used to compare YAP mRNA levels. The HepG2215_R-derived xenograft in SCID mice was used as an in vivo model. HCC tissues from a patient with sorafenib failure were used to examine differences in YAP and IGF-R signaling. Results: Positive associations exist among the levels of YAP, IGF-1R, and EMT markers in HCC tissues and the levels of these proteins increased with sorafenib failure, with a trend of tumor-margin distribution in vivo. Blocking YAP downregulated IGF-1R signaling-related proteins, while IGF-1/2 treatment enhanced the nuclear translocation of YAP in HCC cells through PI3K-mTOR regulation. The combination of YAP-specific inhibitor verteporfin (VP) and sorafenib effectively decreased cell viability in a synergistic manner, evidenced by the combination index (CI). Conclusion: A YAP-IGF-1R signaling loop may play a role in HCC sorafenib resistance and could provide novel potential targets for combination therapy with sorafenib to overcome drug resistance in HCC.