Integrity of the LXXLL motif in Stat6 is required for the inhibition of breast cancer cell growth and enhancement of differentiation in the context of progesterone

Abstract

BackgroundProgesterone is essential for the proliferation and differentiation of mammary gland epithelium. Studies of breast cancer cells have demonstrated a biphasic progesterone response consisting of an initial proliferative burst followed by sustained growth arrest. However, the transcriptional factors acting with the progesterone receptor (PR) to mediate the effects of progesterone on mammary cell growth and differentiation remain to be determined. Recently, it was demonstrated that signal transducer and activator of transcription 6 (Stat6) is a cell growth suppressor. Similar to progesterone-bound PR, Stat6 acts by inducing the expression of the G1 cyclin-dependent kinase inhibitors p21 and p27. The possible interaction between Stat6 and progesterone pathways in mammary cells was therefore investigated in the present study.MethodsChIP and luciferase were assayed to determine whether Stat6 induces p21 and p27 expression by recruitment at the proximal Sp1-binding sites of the gene promoters. Immunoprecipitation and Western blotting were performed to investigate the interaction between Stat6 and PR-B. The cellular DNA content and cell cycle distribution in breast cancer cells were analyzed by FACS.ResultsWe found that Stat6 interacts with progesterone-activated PR in T47D cells. Stat6 synergizes with progesterone-bound PR to transactivate the p21 and p27 gene promoters at the proximal Sp1-binding sites. Moreover, Stat6 overexpression and knockdown, respectively, increased or prevented the induction of p21 and p27 gene expression by progesterone. Stat6 knockdown also abolished the inhibitory effects of progesterone on pRB phosphorylation, G1/S cell cycle progression, and cell proliferation. In addition, knockdown of Stat6 expression prevented the induction of breast cell differentiation markers, previously identified as progesterone target genes. Finally, Stat6 gene expression levels increased following progesterone treatment, indicating a positive auto-regulatory loop between PR and Stat6.ConclusionsTaken together, these data identify Stat6 as a coactivator of PR mediating the growth-inhibitory and differentiation effects of progesterone on breast cancer cells.

Uncovering a Dual Regulatory Role for Caspases During Endoplasmic Reticulum Stress-induced Cell Death

“…During ER stress, STAT6 is cleaved and unlike CREB1 and SRF, the protein is not degraded but rather is present as a stable, lower molecular weight fragment. Based on antibody epitope and molecular weight shift by Western blot we have determined that cleavage of STAT6 results in a loss of the C terminus including the LXXLL motif known to be important for dimerization with transcriptional co-regulatory proteins ( 58 , 59 ). This truncated STAT6 may potentially act as a dominant negative because the protein homodimerizes during transcriptional activation.…”

Prognostic significance of neutrophil-to-lymphocyte ratio in prostate cancer: evidence from 16,266 patients

“…Growing evidence has indicated that inflammatory response could be heavily involved in the occurrence and development of different cancer types 26 27 28 . Studies revealed that inflammation-related neutrophils and immunocytes including lymphocytes were indispensable participants in tumorigenesis 29 .…”

STAT6 deficiency ameliorates Graves’ disease severity by suppressing thyroid epithelial cell hyperplasia

“…We also revealed that the STAT6 target Bcl-xL was responsible for inhibiting apoptosis and that cyclin-D1 was a key factor in cell proliferation. Other proteins, such as Bcl-2, Bax, Bad, p21, p27 kip1 and PCNA, are likely to be important contributors to cell growth, 19, 21, 22, 24, 32, 33, 34, 35, 36 but our experiments showed that the expression of these genes did not change in TECs from EAGD mice or patients (data not shown). Notably, the cytokines responsible for activating p-STAT6 are diverse.…”