1,25-DIHYDROXYVITAMIN-D3 INCREASES THE CELLULAR CONTENT OF THE CALCIUM-ACTIVATED NEUTRAL PROTEASE MU-CALPAIN IN RENAL-CELL CARCINOMA

mu-Calpain is a calcium-dependent neutral thiol protease activated by micromolar concentrations of calcium. mu-Calpain is implicated in vari ous cellular functions regulated by calcium including exocytosis, cell fusion, apoptosis and control of cell proliferation. We studied the e ffect of 1,25-(OH)(2)D-3 on mu-calpain levels in the human renal cell carcinoma line SK-RC-29 using monoclonal antibodies to the 80 kDa subu nit of tr-calpain. Exposure of low density cultures (15000 cells/cm(2) ) to 1,25-(OH)(2)D-3 (100nM) for 48 hours resulted in 1.5-3 fold incre ase of mu-calpain cell content. The effect was not observed in higher density cultures (40000 cells/cm(2)). mu-Calpain content of high densi ty cultures was higher than that of low density cultures and similar t o that in low density cultures treated by 1,25-(OH)(2)D-3. The cellula r content of two other calcium binding proteins, annexin II and annexi n VI was not affected by the hormone. 1,25-(OH)(2)D-3 did not affect c ell number or viability therefore its effect on mu-calpain is not seco ndary to changes in cell density. The effect of 1,25-(OH)(2)D-3 was do se-dependent apparent already at 1nM and was not observed with 24,25-( OH)(2)D-3. Increase in mu-calpain content may underlie some of the act ions of 1,25-(OH)(2)D-3 on classical and non classical target cells.