In support of this notion, we show here that the CGs in the 5' promoter region of the caveolin-1 gene are functionally methylated in two human breast cancer cell lines (MCF7 and T-47D) that fail to express the caveolin-1 protein.
These results provide, for the first time, genetic evidence that a functioning Caveolin-1 mutation may have a role in the malignant progression of human breast cancer.
To understand the role of the Cav-1 (P132L) mutation in the pathogenesis of human breast cancers, we generated the same mutation in wild-type (WT) Cav-1 and studied its behavior in cultured cells.
For example, the human CAV-1 gene maps to a suspected tumor suppressor locus (D7S522/7q31.1) that is frequently deleted in a number of carcinomas, including breast cancers.
We introduced the caveolin-1 gene into a MCF-7 human breast cancer cell line, and examined its cell growth, cell viability, and anchorage-independent growth.
Results showed higher HER2/neu mRMA levels and lower CAV1 and CAV2 mRMA levels in breast cancer tissues than in corresponding normal tissues (P<0.001).
Further analysis by EST vNorthern and virtual microarray analysis reduced the candidate genes to six, with four down-regulated genes, ANXA1, CAV1, KRT5 and MMP7, and two up-regulated genes, ERBB2 and G1P3 in breast cancer.
Genetic evidence from the study of Cav-1(-/-) null mice and human breast cancer mutations [CAV-1 (P132L)] supports the idea that caveolin-1 normally functions as a negative regulator of cell transformation and mammary tumorigenesis.
Dose-response studies showed that the growth inhibition seen at lower concentrations of CDDO correlated with induction of the tumor suppressor gene caveolin-1, which is known to inhibit breast cancer cell growth.
The role of caveolin 1 (CAV1), a structural component of caveolae in breast cancer is controversial, although most studies suggest that it functions as a tumor-suppressor gene.
Messenger RNA expression levels of excision repair cross complementing 1 (ERCC1), breast cancer 1 (BRCA1), ribonucleotide reductase subunit M1 (RRM1) and caveolin-1 were determined by RT-PCR in tumor DNA from 57 advanced and metastatic bladder cancer patients treated with either gemcitabine/cisplatin or gemcitabine/cisplatin/paclitaxel (Taxol).
We have previously reported that expression of caveolin-1 in stably transfected MCF-7 human breast cancer (MCF-7/Cav1) cells up-regulates phosphorylation of a putative Akt substrate protein, designated pp340 [D. Ravid, S. Maor, H. Werner, M. Liscovitch, Caveolin-1 inhibits cell detachment-induced p53 activation and anoikis by upregulation of insulin-like growth factor-I receptors and signaling, Oncogene 24 (2005) 1338-1347.].
Here we show that augmented caveolin-1 expression in cells with low basal levels of this protein, such as human colon cancer (HT29, DLD-1), breast cancer (ZR75), and embryonic kidney (HEK293T) cells reduced COX-2 mRNA and protein levels and beta-catenin-Tcf/Lef and COX-2 gene reporter activity, as well as the production of PGE(2) and cell proliferation.
This work defines a novel role for caveolin-1 with implications for the clinical course of breast cancer and identifies caveolin-1 as a potential drug target for the treatment of early oestrogen-dependent breast cancers.