Midregion PTHrP regulates Rip1 and caspase expression in MDA-MB231 breast cancer cells.

It was previously reported that the midregion PTHrP domain (38-94)-amide restrains growth and invasion "in vitro", causes striking toxicity and accelerates death of some breast cancer cell lines, the most responsive being MDA-MB231 whose tumorigenesis was also attenuated "in vivo". In addition, we have demonstrated that midregion PTHrP is imported in the nucleoplasm of cultured MDA-MB231 cells, and that "in vitro" it can bind chromatin of metaphase spread preparations and also an isolated 20-mer oligonucleotide, thereby appearing endowed with a putative transcription factor-like DNA-binding ability. Here, we examined whether PTHrP (38-94)-amide was able to modulate the expression of genes encoding for apoptosis factors and caspases. Employing a combination of conventional and semi-quantitative multiplex PCR techniques, antisense oligonucleotide (asODN) transfections, proliferation/invasion assays and protein analyses, here we report that PTHrP treatment induces the up-regulation of Bcl-xS, Bad and Rip1 and switches-on the expression of caspase-2, -5, -6, -7 and -8 in MDA-MB231 cells. Moreover, we demonstrate for the first time that asODN-induced under-expression of Rip1 can lead to a more pronounced up-regulation of some caspases due, at least in part, to JNK inactivation, thus providing a new example of factor involved in the transcriptional regulation of the apoptotic enzymes.