No abstract

PC cell-derived growth factor, also known as progranulin, is an M r 88,000 growth factor (referred as PCDGF/GP88) overexpressed in human breast cancer. Antisense inhibition of PCDGF/GP88 expression in MDA-MB-468 cells inhibited tumor formation in nude mice. In estrogen receptor-positive cells, PCDGF/GP88 was expressed in response to estradiol and shown to mediate its mitogenic effect. Pathologic studies indicated that PCDGF/GP88 was expressed in 80% of invasive ductal carcinomas in correlation with parameters of poor prognosis. In the present article, the relationship between PCDGF/GP88 expression and tamoxifen resistance was examined in MCF-7 cells. PCDGF/GP88 overexpression rendered MCF-7 cells able to proliferate in the absence of estrogen and in the presence of tamoxifen. The PCDGF/GP88-overexpressing cells formed tumors in ovariectomized nude mice in the absence of estradiol and in its presence, in contrast to MCF-7 cells. Tumor growth of the overexpressing cells was increased significantly when the mice were treated with tamoxifen. PCDGF/GP88 blocked tamoxifen-induced apoptosis by preventing down-regulation of bcl-2 expression and poly(ADP-ribose) polymerase cleavage. In addition, PCDGF/GP88-overexpressing cells presented higher level of the angiogenic factors vascular endothelial growth factor and angiopoietin-1 than MCF-7 control cells. Tamoxifen treatment additionally increased the level of vascular endothelial growth factor. These studies suggest that PCDGF/GP88 plays a critical role in breast cancer tumorigenesis and in the transition to estrogen independence and tamoxifen resistance, a hallmark of poor prognosis. On the basis of the in vivo studies, it is postulated that tamoxifen treatment of patients with estrogen receptor-positive breast tumors overexpressing PCDGF/GP88 could have adverse clinical consequences.

NgR1, NgR2, and NgR3 which constitute the Nogo-66 receptor family are primarily expressed by neurons in the central nervous system (CNS) and believed to limit axonal growth and sprouting following CNS injury. In an attempt to define the expression and decipher the function of individual members of the Nogo-66 receptor family, we previously reported the generation of selective rabbit polyclonal antibodies. Here we exploit the same immune repertoires by phage display technology to generate rabbit monoclonal antibodies (mAbs) with nanomolar affinity to epitopes that are specific for NgR1 and NgR2, respectively, but at the same time conserved between mouse, rat, and human orthologs. Employing phage display vector pC3C, a newly designed phagemid optimized for the generation and selection of Fab libraries with human constant domains, rabbit mAbs were selected from chimeric rabbit/human Fab libraries, characterized in terms of specificity, affinity, and amino acid sequence, and finally converted to chimeric rabbit/human IgG. Using immunofluorescence microscopy and immunoprecipitation, we demonstrate strong and specific recognition of cell surface bound Nogo-66 receptor family members by chimeric rabbit/human IgG. The rabbit mAbs reported here together with their amino acid sequences constitute a defined panel of species cross-reactive reagents in infinite supply which will aid investigations toward a functional role of the Nogo-66 receptor family in and beyond the CNS.