The AIB1 oncogene promotes breast cancer metastasis by activation of PEA3-mediated matrix metalloproteinase 2 (MMP2) and MMP9 expression. Mol Cell Biol. 2008;28:5937-5950. [PMID: 18644862 DOI: 10.1128/MCB.00579-08]

Overexpression of the N-terminal 24-amino acid domain of p55γ regulatory subunit of PI3K inhibits the migration of human gastric carcinoma MGC803 cells

AIM: To investigate the effects of overexpression of the N-terminal 24-amino acid domain of p55γ regulatory subunit (N24p55γ) of phosphoinositide 3-kinase (PI3K) on the migration of human gastric carcinoma MGC803 cells.

METHODS: MGC803/GFP-N24 and MGC803/GFP cell lines stably expressing N24p55γ-GFP fusion protein (GFP-N24) and GFP protein alone were generated by transfection of MGC803 cells with pEGFPN24 plasmid and control plasmid pEGFPC1, respectively. The impact of GFP-N24 overexpression on cell motility and migration was detected by wound healing assay and Transwell migration assay. The expression and secretion of tumor metastasis-related protein matrix metalloproteinase-9 (MMP9) were determined by gelatin zymography. The effect of GFP-N24 overexpression on the activity of the PI3K-Akt signaling pathway was analyzed by Western blot.

RESULTS: The MGC803/GFP-N24 cell line steadily expressing the GFP-N24 fusion protein and the MCG803/GFP cell line steadily expressing GFP were successfully established. The results of wound healing assay and Transwell migration assay showed that the in vitro migration of MGC803/GFP-N24 cells was restricted (t = 0.003, P < 0.01). GFP-N24 overexpression inhibited the activity of PI3K-Akt signaling pathway by decreasing the expression of phospho-Akt in MGC803 cells. However, GFP-N24 overexpression did not alter the expression and secretion of MMP9 protein.

CONCLUSION: Ectopic expression of N24p55γ inhibits cell migration in vitro by suppressing the activity of the PI3K-Akt signaling pathway in MGC803 cells. The N24p55γ peptide can potentially be used to treat gastric carcinoma.

The roles and action mechanisms of p160/SRC coactivators and the ANCCA coregulator in cancer

Chromosomal aberrations involving genes encoding members of the p160/SRC transcriptional coactivator family such as AIB1/ACTR and TIF2 implicated the coactivators in malignancy of human cells. Significant progress has been made in the last decade toward uncovering their roles in the development and progression of solid tissue tumors as well as leukemia and understanding of the underlying molecular mechanisms. Here, we review their genetic aberrations and dysregulation in expression in breast cancer, prostate cancer, and other nonhormone-responsive cancers. The experimental evidence gathered from studies using cell culture and animal models strongly supports a critical and, in some circumstances, their oncogenic function. We summarize results that the SRCs may contribute to tumorigenesis and disease progression through transcription factors such as E2F, PEA3, and AP-1 and through an intimate control of signaling pathways of growth factors-Akt and the receptor tyrosine kinases. The finding that a recently identified nuclear receptor coregulator ANCCA, like the SRCs, is frequently overexpressed in many types of cancers again underscores their broader roles in cancer.

Lessons in signaling and tumorigenesis from polyomavirus middle T antigen

The small DNA tumor viruses have provided a very long-lived source of insights into many aspects of the life cycle of eukaryotic cells. In recent years, the emphasis has been on cancer-related signaling. Here we review murine polyomavirus middle T antigen, its mechanisms, and its downstream pathways of transformation. We concentrate on the MMTV-PyMT transgenic mouse, one of the most studied models of breast cancer, which permits the examination of in situ tumor progression from hyperplasia to metastasis.

Normal and cancer-related functions of the p160 steroid receptor co-activator (SRC) family

The three homologous members of the p160 SRC family (SRC1, SRC2 and SRC3) mediate the transcriptional functions of nuclear receptors and other transcription factors, and are the most studied of all the transcriptional co-activators. Recent work has indicated that the SRCgenes are subject to amplification and overexpression in various human cancers. Some of the molecular mechanisms responsible for SRC overexpression, along with the mechanisms by which SRCs promote breast and prostate cancer cell proliferation and survival, have been identified, as have the specific contributions of individual SRC family members to spontaneous breast and prostate carcinogenesis in genetically manipulated mouse models. These studies have identified new challenges for cancer research and therapy.

The role of steroid receptor coactivator-3 (SRC-3) in human malignant disease

BACKGROUND

The p160 steroid receptor coactivator (SRC) family is critical to the transcriptional activation function of nuclear hormone receptors. A key member of this family is SRC-3, initially found to be amplified and expressed in breast cancer it has subsequent been shown to be expressed in malignant disease arising from a wide range of other organs. An understanding of the potential role of SRC-3 in the pathogenesis and its possible prognostic role in a broad range of tumours will improve our general understanding of carcinogenesis as well as potentially leading to a new prognostic marker as well as new therapeutic targets.

METHODS

Relevant papers were identified by searching the PubMed and MEDLINE databases for article published until 28th February 2009. Only articles published in English were considered. The search terms included "SRC-3", "AIB1" in association with the following terms: "human", "cancer" and "malignant disease". The search focused on malignant disease arising outside of the mammary gland. Full articles were obtained and references were checked for additional material when appropriate.

RESULTS

SRC-3 is amplified and expressed in a wide spectrum of human malignant diseases and appears to be a potential prognostic marker in a number of different tumours.

CONCLUSION

SRC-3 appears to be implicated in the possible risk of developing prostate and ovarian cancer. Its presence appears to be a marker of aggressive disease. Further research is required to determine its predictive and prognostic utility given the relative paucity of studies for each specific malignant disease.

The steroid receptor coactivator-1 regulates twist expression and promotes breast cancer metastasis

In breast cancer, steroid receptor coactivator-1 (SRC-1) expression positively correlates with HER2 expression and poor prognosis. In mouse mammary tumor virus-polyoma middle T (PyMT) breast cancer mouse model, SRC-1 strongly promotes mammary tumor metastasis. However, the molecular targets and mechanisms that mediate the role of SRC-1 in metastasis are unknown. In this study, SRC-1 wild-type (WT) and knockout (KO) cell lines were developed from the mammary tumors of WT/PyMT and KO/PyMT mice. WT cells exhibited strong migration and invasion capabilities, reduced E-cadherin and beta-catenin epithelial markers, gained N-cadherin and vimentin mesenchymal markers, and formed undifferentiated invasive structures in three-dimensional culture. In contrast, KO cells showed slow migration and invasion, retained E-cadherin, had less N-cadherin and vimentin, and developed partially differentiated three-dimensional structures. Importantly, WT cells expressed Twist, a master regulator of metastasis, at significantly higher levels versus KO cells. SRC-1 knockdown in WT cells reduced Twist expression, whereas SRC-1 restoration in KO cells also rescued Twist expression. Furthermore, SRC-1 was found to coactivate Twist transcription through physical interaction with the transcription factor PEA3 at the proximal Twist promoter. Accordingly, Twist knockdown in WT cells increased E-cadherin and reduced cell invasion and metastasis, and Twist expression in KO cells decreased E-cadherin and increased cell invasion. SRC-1 knockdown in human breast cancer cells also decreased Twist, cell migration, and invasion. Therefore, SRC-1 promotes breast cancer invasiveness and metastasis by coactivating PEA3-mediated Twist expression. Intervention of SRC-1 function may provide new strategies to inhibit breast cancer metastasis.

The role of SRC-1 in murine prostate cancinogenesis is nonessential due to a possible compensation of SRC-3/AIB1 overexpression

The androgen and androgen receptor (AR)-regulated gene expression plays important roles in normal prostate and prostate cancer development, and AR transcriptional control of genes is mediated by transcriptional coactivators, including the three members of the steroid receptor coactivator (SRC) family, SRC-1 (NCOA1), SRC-2 (TIF2/GRIP1/NCOA2) and SRC-3 (AIB1, ACTR/RAC3/NCOA3). SRC-1 and SRC-3 are overexpressed in multiple human endocrine cancers and knockdown of either one of them in prostate cancer cell lines impedes cellular proliferation. Knockout of SRC-3 in mice suppresses the progression of spontaneous prostate carcinogenesis. In this study, we investigated SRC-1 contribution to prostate cancer in vivo by deleting the SRC-1 gene in TRAMP mice, which contain the probasin promoter-driven SV40 T/t antigen transgene. In assessing tumor mass of mice at various ages, we found that initiation and progression of prostate cancer induced by SV40 T/t antigens were unaltered in SRC-1^-/- mice versus WT mice. Primary tumor histology and metastasis to distant lymph nodes were also similar in these mice at all time points assessed. These results demonstrate that the role of SRC-1 in mouse prostate carcinogenesis is nonessential and different from the essential contribution of SRC-3 that is required for prostate cancer progression and metastasis in mice. Interestingly, we observed that during prostate tumorigenesis SRC-1 expression was relatively constant, while SRC-3 expression was significantly elevated. Therefore, the loss of SRC-1 function may be compensated by SRC-3 overexpression during prostate tumorigenesis in SRC-1^-/- mice.

Disruption of the SRC-1 gene in mice suppresses breast cancer metastasis without affecting primary tumor formation

Steroid receptor coactivator-1 (SRC-1) is a coactivator for nuclear hormone receptors such as estrogen and progesterone receptors and certain other transcription factors such as Ets-2 and PEA3. SRC-1 expression in breast cancer is associated with HER2 and c-Myc expression and with reduced disease-free survival. In this study, SRC-1(-/-) mice were backcrossed with FVB mice and then cross-bred with MMTV-polyoma middle T antigen (PyMT) mice to investigate the role of SRC-1 in breast cancer. Although mammary tumor initiation and growth were similar in SRC-1(-/-)/PyMT and wild-type (WT)/PyMT mice, genetic ablation of SRC-1 antagonized PyMT-induced restriction of mammary ductal differentiation and elongation. SRC-1(-/-)/PyMT mammary tumors were also more differentiated than WT/PyMT mammary tumors. The intravasation of mammary tumor cells and the frequency and extent of lung metastasis were drastically reduced in SRC-1(-/-)/PyMT mice compared with WT/PyMT mice. Metastatic analysis of transplanted WT/PyMT and SRC-1(-/-)/PyMT tumors in SRC-1(-/-) and WT recipient mice revealed that SRC-1 played an intrinsic role in tumor cell metastasis. Furthermore, SRC-1 was up-regulated during mammary tumor progression. Disruption of SRC-1 inhibited Ets-2-mediated HER2 expression and PyMT-stimulated Akt activation in the mammary tumors. Disruption of SRC-1 also suppressed colony-stimulating factor-1 (CSF-1) expression and reduced macrophage recruitment to the tumor site. These results suggest that SRC-1 specifically promotes metastasis without affecting primary tumor growth. SRC-1 may promote metastasis through mediating Ets-2-mediated HER2 expression and activating CSF-1 expression for macrophage recruitment. Therefore, functional interventions for coactivators like SRC-1 may provide unique approaches to control breast cancer progression and metastasis.