The Ras-MAPK pathway downregulates Caveolin-1 in rodent fibroblast but not in human fibroblasts: implications in the resistance to oncogene-mediated transformation

Abstract

Normal human diploid fibroblasts (HDFs) are refractory to oncogene-mediated transformations in vitro, compared with rodent fibroblasts. As successful oncogene-mediated transformations of normal HDFs have been reported using the human telomerase catalytic subunit, it has been considered that telomerase activity contributes to the species-specific transformability. However, these transformed HDFs are much less malignant compared with those of rodent cells, suggesting the existence of undefined mechanisms that render HDFs resistant to malignant transformation. Here, cDNA microarray analysis identified caveolin-1 as one of the possible cellular factors involved in such mechanisms. The mitogen-activated protein kinases (MAPK) pathway downregulates Caveolin-1 in rodent fibroblasts, transformed by coexpression of the SV40 early region and activated H-Ras. In contrast, the coexpression of these two oncogenes in HDFs failed to reduce the expression level of Caveolin-1. These results strongly suggest the presence of critical differences in events following the phosphorylation of ERK during the activation process of the MAPK signaling pathway between human and rodent cells, as the ERK protein was similarly phosphorylated in both systems. Furthermore, the small interfering RNA-mediated suppression of Caveolin-1 facilitated the oncogene-mediated transformation of normal HDFs, clearly indicating that the differences in the transformability between human and rodent cells are due, at least in part, to the mechanism responsible for the resistance to Ras-induced Caveolin-1 downregulation in HDFs.

Caveolin-1 in tumor progression: the good, the bad and the ugly

“…Antisense-mediated downregulation of Cav1 induces cell transformation and anchorage-independent growth of NIH-3T3 fibroblasts, along with tumor formation in athymic mice, and significant loss of caveolae expression [105]. Conversely, resistance to oncogene-mediated transformation in human fibroblasts was found to be due to a failure of MAPK-mediated downregulation of Cav1 expression [106]. Depletion of Cav1 inhibits the anchorageindependent growth of Ewing's sarcoma (EWS) cells and also significantly reduces the growth of EWS cell-derived tumors in nude mice xenografts [107].…”

Caveolin-1: a marker for pancreatic cancer diagnosis

“…Cav-1 was shown to inhibit the endothelial nitric oxide synthase (eNOS) pathway, involved in endothelial cell proliferation and angiogenesis [41]. It acts as an endogenous inhibitor of the Ras-p42/44-MAP kinase signaling cascade [32,33,42,43] and inhibits signaling from EGF receptor, Raf-1, MEK-1, PKC and Erk-2 to the nucleus [43,44].…”

Medulloblastomas Derived from Cxcr6 Mutant Mice Respond to Treatment with a Smoothened Inhibitor

“…Primer sequences used in this experiment included 5 ¶-ATGTT-TGCCCCAACAGATG-3 ¶ and 5 ¶-CTAGAGTTGGAACATACTGGTGG-3 ¶ for mouse Cxcr6 and 5 ¶-ATGGAAGATCCCGTCGTTTTAC-3 ¶ and 5 ¶-ATGGGATAGGTCACGTTGGTG-3 ¶ for lacZ. PCR primers for glyceraldehyde-3-phosphate dehydrogenase (Gapdh) were previously described (32).…”