Human CALB2 blocking peptide

Calretinin, a Ca2+-binding protein, participates in many cellular events. Our previous studies found the high expression of calretinin in testicular Leydig cells. In this study, (MLTC-1 cells were infected with LV-calb2, R2C cells with LV-siRNA-calb2. The primary mouse Leydig cells were also used to confirm those data from cell lines. Testosterone level was significantly higher in the MLTC-1 cells with over-expressed calretinin than in the control, while progesterone was lower in the R2C cells in which down-regulated calretinin. The expressions of StAR changed in synchrony with hormones. Cytoplasmic Ca2+ level was significantly increased when calretinin was over-expressed. When MLTC-1 cells were infected with LV-calb2 and then stimulated using Clopiazonic, a Ca2+-releasing agent, testosterone was significantly increased. Interestingly, the expression levels of PLC, p-PKC mu (PKD), p-MARCKS and CREB, were significantly increased in the MLTC-1 cells with over-expressed calretinin, while PLC, p-PKD, p-MARCKS, MARCKS and CREB were decreased in the R2C cells with down-regulated calretinin. We also observed the increased expression of calretinin up-regulated testosterone production and the expressions of StAR and PLC in primary mouse Leydig cells. So, calretinin as a Ca2+-binding protein participates in the regulation of steroidogenesis via the PLC-Ca2+-PKC pathway in Leydig cells.

Calretinin (CR; CALB2) belonging to the family of EF-hand Ca2+-binding proteins (CaBP) is widely used as a positive marker for the identification of human malignant mesothelioma (MM) and functionally was suggested to play a critical role during carcinogenesis of this highly aggressive asbestos-associated neoplasm. Increasing evidence suggests that CR not only acts as a prototypical Ca2+ buffer protein, i.e., limiting the amplitude of Ca2+ signals but also as a Ca2+ sensor. No studies have yet investigated whether other closely related CaBPs might serve as substitutes for CR's functions(s) in MM cells. Genetically modified MM cell lines with medium (MSTO-211H and ZL5) or low (SPC111) endogenous CR expression levels were generated that overexpress either CR's closest homologue calbindin-D28k (CB) or parvalbumin (PV), the latter considered as a "pure" Ca2+ buffer protein. After lentiviral shCALB2-mediated CR downregulation, in both MSTO-211H and ZL5 cells expressing CB or PV, the CR deficiency-mediated increase in cell death was not prevented by CB or PV. With respect to proliferation and cell morphology of SPC111 cells, CB was able to substitute for CR, but not for CR's other functions to promote cell migration or invasion. In conclusion, CR has a likely unique role in MM that cannot be substituted by "similar" CaBPs.