Collectively, these studies suggest that targeting PTHrP expression in the tumor cells could be a potential therapeutic strategy for breast cancers, especially those with skeletal metastases.
Because the stromal component of the breast produces factors implicated in proliferation and differentiation of mammary epithelial tissue and tumors, the aim of this study was to investigate the PTHrP expression by mammary fibroblasts from breast cancer tumors and normal breast.
Prolactin stimulated PTHrP transcript and protein in breast cancer cell lines <i>in vitro</i> and <i>in vivo</i>, effects mediated by Stat5 through the P2 gene promoter, producing transcript AT6 encoding the PTHrP 1-173 isoform.
The role of PTHrP in breast cancer growth and metastasis may thus be mediated via upregulation of integrin alpha6beta4 expression and Akt activation, with consequent inactivation of GSK-3.
Immunohistochemistry was used to examine PTHrP and TGF-β protein expression in 497 cases of early breast cancer, and Kaplan-Meier method and COX's Proportional Hazard Model were applied to the prognostic value of PTHrP and TGF-β expression.
Although the PTHRP-receptor (PTHRP-R) is often coexpressed with PTHRP in PBC, its role in regulating breast cancer cell proliferation and metastases to bone remains unclear.
The statistical analysis revealed that PTHRP- and KRT19-positive detections correlated with the diagnosis of breast cancer while the combined positive detections of PTHRP-plus-KRT19 correlated with the presence of distant metastasis, especially with bone metastasis.
Together, by controlling the expression of PTHrP and its downstream OPG/RANKL, TF-SB has significant inhibition effects on breast cancer bone metastasis, which indicates a new therapeutic method.
RNA interference of endogenous PTHrP caused a significant reduction in cell adhesion of a breast cancer cell line to collagen type I, fibronectin and laminin (P<0.05) and of a colon cancer cell to collagen type I and fibronectin (P<0.05).
These findings establish that PTHrP is commonly synthesized by primary breast cancers and support previous immunohistochemical studies reporting a higher incidence of PTHrP-positive tumor cells in skeletal metastases than in nonskeletal metastases.
Two of the loci lie in regions that contain strong plausible candidate genes: PTHLH (12p11) has a crucial role in mammary gland development and the establishment of bone metastasis in breast cancer, and NRIP1 (21q21) encodes an ER cofactor and has a role in the regulation of breast cancer cell growth.
Now, research into the basic biology of PTHrP has suggested previously unrecognized connections to a variety of disease states such as osteoporosis, osteoarthritis, and breast cancer and has highlighted how PTHrP itself might be used in therapy for osteoporosis and diabetes.