PGRMC1 and breast cancer: Additional evidence of the existence of a negative regulatory pathway downstream of PGRMC1, which depends on PKA activation results of the evaluation of the level of P-VASP, being the phosphorylation of VASP, impaired in MDA-MB-231 cells lacking PGRMC1 (See Figure 6B), might support the existence of a P4/PGRMC1/cAMP/PKA signaling pathway in breast cancer cells, modulating the P4-evoked Ca2+ entry via phosphorylation of Orai1 by PKA, as previously reported [43,44].