Heparin-binding EGF-like growth factor in the human prostate: Synthesis predominantly by interstitial and vascular smooth muscle cells and action as a carcinoma cell mitogen

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Abstract
Heparin‐binding epidermal growth factor‐like growth factor (HB‐EGF) is an activating ligand for the EGF receptor (HER1/ErbB1) and the high‐affinity receptor for diphtheria toxin (DT) in its transmembrane form (proHB‐EGF). HB‐EGF was immunolocalized within human benign and malignant prostatic tissues, using monospecific antibodies directed against the mature protein and against the cytoplasmic domain of proHB‐EGF. Prostate carcinoma cells, normal glandular epithelial cells, undifferentiated fibroblasts, and inflammatory cells were not decorated by the anti‐HB‐EGF antibodies; however, interstitial and vascular smooth muscle cells were highly reactive, indicating that the smooth muscle compartments are the major sites of synthesis and localization of HB‐EGF within the prostate. In marked contrast to prostatic epithelium, proHB‐EGF was immunolocalized to seminal vesicle epithelium, indicating differential regulation of HB‐EGF synthesis within various epithelia of the reproductive tract. HB‐EGF was not overexpressed in this series of cancer tissues, in comparison to the benign tissues. In experiments with LNCaP human prostate carcinoma cells, HB‐EGF was similar in potency to epidermal growth factor (EGF) in stimulating cell growth. Exogenous HB‐EGF and EGF each activated HER1 and HER3 receptor tyrosine kinases and induced tyrosine phosphorylation of cellular proteins to a similar extent. LNCaP cells expressed detectable but low levels of HB‐EGF mRNA; however, proHB‐EGF was detected at the cell surface indirectly by demonstration of specific sensitivity to DT. HB‐EGF is the first HER1 ligand to be identified predominantly as a smooth muscle cell product in the human prostate. Further, the observation that HB‐EGF is similar to EGF in mitogenic potency for human prostate carcinoma cells suggests that it may be one of the hypothesized stromal mediators of prostate cancer growth. J. Cell. Biochem. 68:328‐338, 1998.

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