Anti-metastatic outcome of isoform-specific prolactin receptor targeting in breast cancer

Abstract

Controversy exists concerning the role of the long prolactin receptor (PRLR) in the progression of breast cancer. By targeting pre-mRNA splicing, we succeeded in knocking down only the long PRLR in vivo, leaving the short forms unaffected. Using two orthotopic and highly-metastatic models of breast cancer, one of which was syngeneic (mouse 4T1) to allow assessment of tumor-immune interactions and one of which was endocrinologically humanized (human BT-474) to activate human PRLRs, we examined the effect of long PRLR knockdown on disease progression. In both models, knockdown dramatically inhibited metastatic spread to the lungs and liver and resulted in increased central death in the primary tumor. In the syngeneic model, immune infiltrates in metastatic sites were changed from innate inflammatory cells to lymphocytes, with an increase in the incidence of tumor-specific cytotoxic T cells. Long PRLR knockdown in three-dimensional culture induced apoptosis of tumor-initiating/cancer stem cells (death of 95% of cells displaying stem cell markers in 15 days). We conclude that the long PRLR plays an important role in breast cancer metastasis.

Prolactin receptor in breast cancer: marker for metastatic risk

“…PRL and the long form of the PRLR also contribute to the metastatic process (Yonezawa et al 2015). These results are consistent with the reports of PRLR-mediated chemotherapeutic resistance (Howell et al 2008, LaPensee et al 2009) and the role of PRL-PRLR in osteolytic bone metastases of breast cancer cells (Sutherland et al 2016).…”

“…These in vitro results obtained from 2D cell culture are in agreement with the work by Barcus and coworkers, who demonstrated that breast cancer cells in compliant (vs stiff) collagen matrices activated JAK2-Stat5 signaling rather than MAPK signaling. The microenvironment would explain the in vivo results recently reported, which show that the PRLR long form is important in metastasis (Yonezawa et al 2015).…”

“…Interestingly, specific knockdown of the long isoform resulted in a sharp decrease in metastatic colonization of the lungs and liver from orthotopic mammary fat pad transplants of syngeneic 4T1 cells in Balb/c mice. The observations were replicated in a humanized xenograft model, using BT474 cells in non-obese diabetic severe combined immunodeficiency (NOD-SCID) mice (Yonezawa et al 2015) (BT474, luminal B-like with Her2 overexpression (Neve et al 2006, Prat et al 2013). …”

“…Although there is a known association of PRL levels with invasive breast cancer, information about the role of PRL in metastasis has been lacking until recently (Yonezawa et al 2015, Sutherland et al 2016. We recently reported the involvement of PRL signaling in breast cancer bone metastases ( Fig.…”

“…Recently, the role of the long PRLR isoform was investigated (Yonezawa et al 2015). Splice-modulating oligomers were delivered in vivo to block splicing between Prlr exons 9 and 10, reducing the amount of the fulllength PRLR, but not SF1a-c, and not of the related growth hormone receptor.…”