APRIL promotes cell cycle progression in primary multiple myeloma cells: influence of D-type cyclin group and translocation status

A proliferation-inducing ligand (APRIL) promotes survival and drug resistance in multiple myeloma (MM) cell lines. We studied the effect of APRIL on cell-cycle behavior in primary MM cells and correlated our findings with D-type cyclin expression by immunohistochemistry and/or Western blotting. In MM cases, expressing cyclin D2 APRIL significantly increased the percentage of CD138+ cells in S + G2/M phase (from 8.4% ± 1.9% to 14.3% ± 2.6%, n = 15, P < .01), whereas a lesser effect was seen in cases expressing cyclin D1 (n = 18). Cell-cycle response to APRIL was most marked for cyclin D2-expressing cases with IgH translocations ( P < .01) and was accompanied by increased expression of cyclin D2, CDK4, CDK6, and phospho-retinoblastoma protein. Cell-cycle proteins in cyclin D1+ cells were not modulated by APRIL. Surface expression of B-cell maturation antigen and transmembrane activator and calcium-modulating cyclophilin ligand interactor was not significantly different between cyclin D1+ and D2+ MM cells. We observed activation of nuclear factor-κB and PI3-kinase pathways in response to APRIL in both cyclin D1+ and D2+ MM cells. In conclusion, APRIL stimulates G1/S progression in cyclin D2+ MM cells bearing IgH translocations but has minimal effect on cyclin D1+ cells, suggesting MM cells from different cyclin D/translocation classes rely on different mechanisms for cell-cycle re-entry.