Up-regulation of prosaposin by the retinoid HPR and its effect on ceramide production and integrin receptors.

Abstract

SPECIFIC AIMSN-(4-hydroxyphenyl)retinamide (HPR) is a synthetic retinoid of clinical use in breast cancer chemoprevention. To understand its mechanism of action, we undertook cDNA differential display analysis to identify genes specifically regulated by HPR.PRINCIPAL FINDINGS1. HPR up-regulates prosaposin gene expressionThe c-DNA differential display screening was performed on mRNA extracted from T47D and MCF7 breast cancer cell lines treated or not for 24 h with 3 μM HPR. One RT-PCR band whose intensity was particularly elevated after retinoid exposure was excised from the gel and tested on Northern blots, where it hybridized to a transcript of ∼1.6 kb. Most important, the intensity of the signal was ∼2.4- to 3.0-fold higher after HPR treatment. The DNA sequence analysis of this RT-PCR band revealed homology with prosaposin, a gene coding for a multifunctional glycoprotein, precursor of four saposins that are localized partly within lysosomes, acting as a cofactors for sphingolipids hydrolysis, and partl...