CLONAL HETEROGENEITY OF THE GROWTH AND INVASIVE RESPONSE OF A HUMAN BREAST-CARCINOMA CELL-LINE TO PARATHYROID HORMONE-RELATED PEPTIDE-FRAGMENTS

It has been previously reported that 8701-BC cells, derived from a pri mary carcinoma of the breast, constitutively express parathyroid hormo ne (PTH)-related peptide (PTHrP) and PTH/PTHrP receptor (PTH/PTHrP-R) genes, that N-terminal, mid-regional and C-terminal immunoreactive PTH rP can be found in cell conditioned medium and, furthermore, that exog enously added PTHrP (1-34), (67-86) and, to a minor extent, (107-139) are anti-mitogenic but promote Matrigel invasion by this cell line, It has also been reported that PTHrP gene expression is selectively swit ched on in those 8701-BC clonal lines endowed with a higher proliferat ion rate and invasive ability in vitro, Here we have first examined th e presence of PTH/PTHrP-R transcript in the different 8701-BC clones b y PCR and Southern blot analysis, Second, we have studied the growth a nd invasive response in vitro to PTHrP fragments by some of these clon es, i.e. BC-3A, BC-61 and BC-66, selected on the basis of their lower (BC-3A) or higher (BC-1 and BC-66) Matrigel invasion ability and their expression of PTHrP (positive for BC-61 and BC-66) and PTH/PTHrP-R (p ositive for BC-61). Our data show the existence of clonal heterogeneit y for PTH/PTHrP-R mRNA and for the proliferative and invasive response s elicited by treatment with diverse PTHrP fragments, In particular: ( i) the sensitivity to PTHrP (1-34) is restricted due to the uneven exp ression of PTH/PTHrP-R; (ii) BC-3A cells (the less 'aggressive' clone) are resistant to the anti-mitogenic effect of the PTHrP domains and, most noticeably, exhibit a growth-potentiating response to PTHrP (67-8 6) opposite to that found for both the parental 8701-BC cells and the two other clones; (iii) all PTHrP fragments tested induced the express ion of a growth-restraining and invasion-promoting phenotype by BC-61 cells (one of the more 'aggressive' clones). Present data in vitro sup port the hypothesis that in vivo PTHrP may be a keg element in local c ontrol of the invasive process during breast carcinoma development and that its role may be, in turn, dependent upon the biological characte ristics and the level of malignancy of the target cells within the mul ticlonal population of a primary tumour.