Caveolin-1, -2, and -3 are the principal
proteins of caveolae, the vesicular invaginations of the plasma membrane. Recent studies suggest that
caveolins play an important role in cellular signaling and, possibly, in
tumorigenesis. We examined the expression of the three
caveolins in
azoxymethane-induced rat
colon adenocarcinoma and normal-appearing colonic mucosa, and also in human
colon cancer cells with inherently different proliferation rates. Expression of
caveolins was assessed in experimental rat
colon adenocarcinoma and normal-appearing colonic tissues by RT-PCR, immunoblot and immunohistochemistry. Expression of
caveolin-1, -2, and -3 at
protein and
mRNA levels in human
colon cancer cell lines Caco-2, HT-29 and HCT-116 was assessed by immunoblot and RT-PCR, respectively. While
caveolin-1 was overexpressed in all experimental
adenocarcinoma tissues by comparison to normal-appearing colonic mucosa at both the
mRNA and
protein level,
caveolin-2 was expressed equally only at the
mRNA level in both tissues. Immunohistochemical analysis of experimental rat colon tissues also revealed a similar pattern with
caveolin-1 being overexpressed in
adenocarcinomas as compared to normal-appearing colonic mucosa.
Caveolin-1 protein expression was observed in HT-29 and HCT-116 cell lines but not in the Caco-2 cell line or the macrophage Raw 264.7 cell line.
Caveolin-1 mRNA expression was evident in all colon
carcinoma cell lines tested; however,
caveolin-2 mRNA was found only in HT-29 and HCT-116.
Caveolin-1 protein and
mRNA transcript levels in human
colon cancer cell lines were observed to be concordant with the growth rate of the cells, and followed the pattern of HCT-116 > HT-29 > Caco-2. Taken together, our results indicate that
caveolin-1 is overexpressed in experimental
colon adenocarcinoma by comparison to adjacent normal mucosa, and its expression in human
colon cancer cells is directly associated with the growth rate.