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Prolactin inhibits BCL6 expression in breast cancer through a Stat5a-dependent mechanism

Thai H Tran1, Fransiscus E Utama, Justin Lin

  • 1Department of Cancer Biology, Kimmel Cancer Center, Philadelphia, Pennsylvania, USA.

Cancer Research
|February 4, 2010
PubMed

Insights

Prolactin, a growth factor, suppresses BCL6 expression in breast cancer via Stat5a signaling. This finding is crucial for understanding breast cancer progression and developing targeted therapies.

Area of Science:

  • Oncology
  • Molecular Biology
  • Cell Signaling

Background:

  • BCL6 is a transcriptional repressor that hinders breast epithelial differentiation and is linked to poorly differentiated breast cancer.
  • Signal transducer and activator of transcription 5 (Stat5a) promotes mammary epithelial differentiation, and its loss correlates with undifferentiated histology and poor prognosis in breast cancer.

Purpose of the Study:

  • To investigate the role of prolactin in regulating BCL6 expression in human breast cancer.
  • To elucidate the signaling pathways involved in prolactin-mediated suppression of BCL6, particularly the involvement of Stat5a.

Main Methods:

  • Utilized human breast cancer cell lines (T47D, MCF7, ZR75.1, SKBr3) to assess BCL6 mRNA and protein levels following prolactin treatment.
  • Employed Stat5a and Stat5b overexpression, constitutively active Stat5a, and chromatin immunoprecipitation assays to determine Stat5's role in BCL6 regulation.
  • Investigated the requirement of MEK-ERK and PI3K-AKT pathways, as well as histone deacetylase activity (using trichostatin A), in prolactin's effect on BCL6.
  • Assessed BCL6 expression in xenotransplant tumors in mice and human breast cancer explants ex vivo.
  • Performed quantitative immunohistochemistry on human breast cancer tissues to correlate BCL6 levels with Stat5a and Stat5b expression and clinicopathological features.

Main Results:

  • Prolactin rapidly suppressed BCL6 mRNA and protein expression in multiple breast cancer cell lines, a process dependent on Stat5a but not Stat5b, MEK-ERK, or PI3K-AKT pathways.
  • Stat5a directly interacted with a BCL6 gene regulatory region, and repression required histone deacetylase activity.
  • BCL6 overexpression interfered with prolactin-induced Stat5 reporter gene activity.
  • Elevated BCL6 levels were observed in high-grade and metastatic breast cancer, correlating negatively with nuclear Stat5a expression.

Conclusions:

  • Prolactin acts as a potent suppressor of BCL6 in human breast cancer, primarily through Stat5a-mediated signaling.
  • The interplay between prolactin, Stat5a, and BCL6 represents a critical regulatory switch in breast cancer, where loss of prolactin-Stat5a signaling promotes an undifferentiated phenotype and poor prognosis.

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