Recombinant Expression of Caveolin-1 in Oncogenically Transformed Cells Abrogates Anchorage-independent Growth

Abstract

Caveolae are plasma membrane-attached vesicular organelles. Caveolin-1, a 21-24-kDa integral membrane protein, is a principal component of caveolae membranes in vivo. Both caveolae and caveolin are most abundantly expressed in terminally differentiated cells: adipocytes, endothelial cells, and muscle cells. Conversely, caveolin-1 mRNA and protein expression are lost or reduced during cell transformation by activated oncogenes such as v-abl and H-ras (G12V); caveolae are absent from these cell lines. However, its remains unknown whether down-regulation of caveolin-1 protein and caveolae organelles contributes to their transformed phenotype.Here, we have expressed caveolin-1 in oncogenically transformed cells under the control of an inducible-expression system. Regulated induction of caveolin-1 expression was monitored by Western blot analysis and immunofluorescence microscopy. Our results indicate that caveolin-1 protein is expressed well using this system and correctly localizes to the plasma membrane. Induction of caveolin-1 expression in v-Abl-transformed and H-Ras (G12V)-transformed NIH 3T3 cells abrogated the anchorage-independent growth of these cells in soft agar and resulted in the de novo formation of caveolae as seen by transmission electron microscopy. Consistent with its antagonism of Ras-mediated cell transformation, caveolin-1 expression dramatically inhibited both Ras/MAPK-mediated and basal transcriptional activation of a mitogen-sensitive promoter. Using an established system to detect apoptotic cell death, it appears that the effects of caveolin-1 may, in part, be attributed to its ability to initiate apoptosis in rapidly dividing cells. In addition, we find that caveolin-1 expression levels are reversibly down-regulated by two distinct oncogenic stimuli. Taken together, our results indicate that down-regulation of caveolin-1 expression and caveolae organelles may be critical to maintaining the transformed phenotype in certain cell populations.

Analysis of the CAVEOLIN-1 gene at human chromosome 7q31.1 in primary tumours and tumour-derived cell lines

“…Signi®cantly, heterologous expression of CAVEOLIN-1 has been shown to suppress ras and v-abl mediated oncogenic transformation of NIH3T3 ®broblasts (Engelman et al, 1997), and independently the anchorage-independent growth of mammary carcinoma-derived cell lines (Lee et al, 1998). We have mapped CAVEOLIN-1 to human chromosome 7q31.1, as a candidate for a multi-tissue tumour suppressor gene that has been localized to this subchromosomal region .…”

“…Further, the extent of reduction in the expression of caveolin correlated with the ability of these oncogenically transformed cells to form colonies in soft-agar (Koleske et al, 1995). Induced expression of caveolin-1 in ras-transformed NIH3T3 cells was shown to abrogate anchorage-independent growth; this was accompanied by inhibition of the ras/raf/MAPK signalling pathway, and by induction of apoptosis (Engelman et al, 1997). Ectopic expression of Caveolin-1 in human breast tumour-derived cell lines has also been shown to suppress in vitro tumour growth (Lee et al, 1998).…”

Reversion of transformed phenotype in ovarian cancer cells by intracellular expression of anti folate receptor antibodies

“…18 Since caveolin-1 acts as a negative regulator of signaling proteins in some normal cell types, 24 its re-expression on ovarian cancer cells might be partially responsible for restoration of growth control. Caveolin-1 re-expression might also be responsible for the acquired anchorage-dependent growth in NIH 3T3 cells 25 and in caveolin-1-transfected IGROV1 cells. 18 Cells with downmodulated FR expression exhibited a significant increase in a6b4 integrin expression and a drastic decrease in laminin production consistent with a reversion of the malignant phenotype.…”

Impact of caveolin-1 expression on prognosis of pancreatic ductal adenocarcinoma

“…Under some conditions, caveolin-1 has been shown to suppress growth of specific cell lines in vitro and in vivo (Koleske et al, 1995;Engelman et al, 1997;Suzuki et al, 1998), and some have suggested that caveolin-1 functions as a tumour suppressor gene (Engelman et al, 1998b). The reasons behind this seemingly contradictory evidence remain unclear.…”