Selective stimulation of prostatic carcinoma cell proliferation by transferrin

Aggressive prostatic carcinomas most frequently metastasize to the skeletal system. We have previously shown that cultured human prostatic carcinoma cells are highly responsive to growth factors found in human bone marrow. To identify the factor(s) responsible for the increased prostatic carcinoma cell proliferation, we fractionated crude bone marrow preparations by using hydroxylapatite HPLC. The major activity peak contained two high molecular weight bands (M(r) = 80,000 and 69,000) that cross-reacted with antibodies to human transferrin and serum albumin, respectively. Bone marrow transferrin, purified to apparent homogeneity by using DEAE-Affi-Gel Blue chromatography, anti-transferrin affinity chromatography, and hydroxylapatite HPLC, markedly stimulated prostatic carcinoma cell proliferation, whereas human serum albumin showed no significant growth factor activity. Marrow preparations, depleted of transferrin by passage over an anti-transferrin affinity column, lost greater than 90% of their proliferative activity. In contrast to the response observed with the prostatic carcinoma cell lines, a variety of human malignant cell lines, derived from other primary sites and metastatic to sites other than bone marrow, showed a reduced response to purified marrow-derived transferrin. These results suggest that rapid growth of human prostatic carcinoma metastases in spinal bone may result from a combination of conditions that include (i) drainage of prostatic carcinoma cells into the paravertebral circulation, (ii) high concentrations of available transferrin in bone marrow, and (iii) increased sensitivity of prostatic carcinoma cells to the mitogenic activity of transferrin.