Modulation of CD99/MIC2 expression of human AHTO-7 osteoblasts by carcinoma cell line-conditioned media

Prostate cancer metastases induce a predominantly osteoblastic response in bone tissue, resulting in new bone formation and associated morbidity; however, the mechanisms of these tumor-host responses are not fully understood.

Supernatants of prostate (PC3, DU145, LNCaP), breast (BT20, ZR-75-1), colon (SW620, Colo 320DM), pancreatic (ASPC1, Capan-1), renal cell (ACHN) and hepatoma (HepG2) cell lines were tested for their capacity to modulate proliferation, activity of alkaline phosphatase (ALP) and CD99/MIC2 expression in AHTO-7 (large T antigen transfected human trabecular osteoblasts) cells in vitro.

Osteoblastic stimulation is not restricted to prostate cancer derived conditioned media CM and high activity is found in CM from Capan-1, HepG2 and ACHN lines. Furthermore these CM down-regulate the expression of the CD99/MIC2 antigen in comparison to medium by AHTO-7 cells as detected by HBA-71 immunofluorescence, with the exception of prostate cancer-derived CM. Induction of the differentiation marker ALP was detected in response to CM derived from Capan-1, BT-20 and Colo320DM. Stimulation of the proliferation of AHTO-7 cells (105-138% of control), induction of ALP (1.17-5.29-fold) and down-regulation of CD99 (13.6-57.5%) exhibited no correlation. CM derived from PC3 and LNCaP metastatic prostate cancer cell lines specifically resulted in the retention/stimulation of the expression of CD99/MIC2 in AHTO-7 cells in contrast to all other cell lines tested.

The CD99/MIC2 antigen, which is expressed on human osteoblasts and osteosarcoma cells, seems to constitute a new and independent response marker of osteoblasts in the triggering of osteoblastic reaction by prostate cancer cells.