CRBP suppresses breast cancer cell survival and anchorage-independent growth

Abstract

We showed earlier that cellular retinol-binding protein (CRBP) expression is downregulated in a subset of human breast cancers. We have now investigated the outcome of ectopic CRBP expression in MTSV1-7 cells, a SV40 T antigen-transformed human breast epithelial cell line devoid of endogenous CRBP expression. We found that: (i) CRBP did not inhibit adherent cell growth but suppressed foci formation in post-con¯uent cultures and colony formation in soft agar; (ii) this e ect was due to CRBP inhibition of cell survival, as demonstrated by viability and TUNEL assays of cells in soft-agar or plated on polyHEMA-coated dishes; (iii) CRBP inhibited protein kinase B/Akt activation in cells in suspension but not in adherent cells and the CRBP suppression of anchorage-independent growth was mimicked by cell treatment with the phosphatidylinositol-3 kinase (PI3K) inhibitor LY294002; (iv) CRBP enhanced retinyl ester formation and storage but did not regulate retinoic acid synthesis or retinoic acid receptor activity. Ectopic CRBP-mediated inhibition of anchorage-independent cell survival and colony formation in the absence of signi®cantly altered responses to either retinol or retinoic acid was also documented in T47D human breast cancer cells. In conclusion, the data suggest two novel and linked CRBP functions in mammary epithelial cells: inhibition of the PI3K/Akt survival pathway and suppression of anchorage-independent growth. Oncogene (2001) 20, 7413 ± 7419.Keywords: FABP; soft agar; anoikis; retinol; retinoic acid CRBP is a 15 kDa cytosolic protein that binds retinol with high a nity and is postulated to regulate the intracellular fate of retinol. For instance, CRBP is known to regulate liver retinol esteri®cation and storage (Ghyselinck et al., 1999) and may also regulate retinol oxidation to retinoic acid in target tissues (Napoli, 1999;Yamamoto et al., 1998). CRBP is widely expressed in epithelial tissues, whereas its homologs, CRBPII and two novel CRBPs have more restricted tissue distributions (Vogel et al., 2000;Folli et al., 2001). CRBPs are the only retinol-binding members of the large family of fatty-acid binding proteins (FABPs; reviewed in Glatz and van der Vusse (1996).We recently reported that human breast carcinogenesis is associated with the loss of CRBP expression in roughly one fourth of breast cancer cases . To begin to investigate the possible signi®cance of this ®nding, we reconstituted CRBP expression in CRBP-negative MTSV1-7 cells and assayed the e ect of this intervention on cell growth. MTSV1-7 (abbreviated MTS) is a human breast ductal epithelial cell line that was immortalized by introduction of the SV40 T antigen (Bartek et al., 1991) and that upon continued culture in our laboratory acquired the ability to form foci and colonies in soft agar (YS Kuppumbatti et al., in preparation). Stable re-expression of CRBP in MTS cells ( Figure 1a) had no e ect on exponential monolayer growth (Figure 1b) but blocked the formation of foci in post-con¯uent cultures ( Figure 1c). Moreover, CRBP re-express...

Sex-Determining Region Y Box 4 Is a Transforming Oncogene in Human Prostate Cancer Cells

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CpG hypermethylation of cellular retinol-binding protein 1 contributes to cell proliferation and migration in bladder cancer

“…The loss of CRBP1 could diminish RA transport and result in blockage of the transcription of RA-responsive genes that regulate cell proliferation. However, previous studies have supported the hypothesis that CRBP1 could be involved in the promotion of apoptosis through an increase in the RA metabolism in breast cancer cell lines (17,24,25). As the suppression of apoptosis played a key role in BC carcinogenesis (26), the observed low expression of CRBP1 in our study could disrupt the RA-mediated apoptosis pathway in BC.…”

“…Many studies have shown that it is down-regulated and functions as a tumor suppressor gene (11)(12)(13)(14)(15)(16)(17)(18), whereas it is up-regulated in cervical cancer (19). In breast cancer, CRBP1 down-regulation promoted the progression of tumors through the inhibition of RA receptor activity (24). In terms of BC, RA treatment effectively reduced the recurrence rate and increased the survival time of superficial BC patients (26,27).…”