14-3-3 sigma, implicated in cell cycle arrest by p53, was cloned by expression cloning through cyclin-dependent kinase 2 (CDK2) association. 14-3-3 sigma shares cyclin-CDK2 binding motifs with different cell cycle regulators, including p107, p130, p21 CIP1 , p27 KIP1 , and p57 KIP2 , and is associated with cyclin⅐CDK complexes in vitro and in vivo. Overexpression of 14-3-3 sigma obstructs cell cycle entry by inhibiting cyclin-CDK activity in many breast cancer cell lines. Overexpression of 14-3-3 sigma can also inhibit cell proliferation and prevent anchorage-independent growth of these cell lines. These findings define 14-3-3 sigma as a negative regulator of the cell cycle progression and suggest that it has an important function in preventing breast tumor cell growth. Cyclin-dependent kinases (CDKs)1 are responsible for the transitions of the eukaryotic cell cycle and are tightly regulated by extra-and intracellular signals. They act in concert with their regulatory subunits, the cyclins, to facilitate the cell cycle progression. The cell cycle regulatory machinery is controlled by both positive and negative regulators. Cyclin-dependent kinases (CDKs) and their cyclin partners are positive regulators or accelerators that help cell cycle progression. The recently characterized cyclin-dependent kinase inhibitors (CKIs) are important negative regulators that act as brakes to stop cell cycle progression in response to regulatory signals (1). Two families of CKIs have been characterized based on the specificity of interaction with CDKs and sequence homology. The CIP/KIP family, which shares homology at the N-terminal CDK inhibitory domain, includes p21 CIP1 / WAF1 (2-5), p27 KIP1

The ubiquitously expressed 14-

Purpose: We have previously shown that PTEN loss confers trastuzumab resistance in ErbB2-overexpressing breast cancer using cell culture, xenograft models, and patient samples. This is a critical clinical problem because trastuzumab is used in a variety of therapeutic regimens, and at the current time, there are no established clinical strategies to overcome trastuzumab resistance. Here, we did preclinical studies on the efficacy of clinically applicable inhibitors of the Akt/ mammalian target of rapamycin (mTOR) pathway to restore trastuzumab sensitivity to PTENdeficient cells. Experimental Design: Cell culture and xenograft models were used to test a panel of clinically applicable, small-molecule inhibitors of the Akt/mTOR signal transduction pathway, a critical pathway downstream of ErbB2, and identify compounds with the ability to restore trastuzumab sensitivity to PTEN-deficient cells. Results: When trastuzumab was combined with the Akt inhibitor triciribine, breast cancer cell growth was inhibited and apoptosis was induced. In a xenograft model, combination therapy with trastuzumab and triciribine dramatically inhibited tumor growth. The combination of trastuzumab and the mTOR inhibitor RAD001also slowed breast cancer cell growth in vitro and in vivo. Conclusions: Combining trastuzumab with inhibitors of the Akt/mTOR pathway is a clinically applicable strategy and combinations of trastuzumab with triciribine or RAD001 are promising regimens for rescue of trastuzumab resistance caused by PTEN loss.

Importance of the field The ubiquitously expressed 14-3-3ζ protein is involved in numerous important cellular pathways involved in cancer. Recent research suggests 14-3-3ζ may play a central role regulating multiple pathways responsible for cancer initiation and progression. This review will provide an overview of 14-3-3 proteins and address the role of 14-3-3ζ overexpression in cancer. Areas covered in this review The review covers the basic role of 14-3-3 in regulation of multiple pathways with a focus on 14-3-3ζ as a clinically relevant biomarker for cancer recurrence. What the reader will gain 14-3-3ζ overexpression has been found in multiple cancers; however, the clinical implications were unclear. Recently, 14-3-3ζ has been identified as a biomarker for poor prognosis and chemoresistance in multiple tumor types, indicating a potential clinical application for using 14-3-3ζ in selecting treatment options and predicting cancer patients’ outcome. Take home message 14-3-3ζ is a potential prognostic marker of cancer recurrence and predictive marker for therapeutic resistance. The overexpression of 14-3-3ζ in multiple cancers suggests that it may be a common target to intervene tumor progression; therefore, more efforts are needed for the development of 14-3-3 inhibitors.

Recent progress in diagnostic tools allows many breast cancers to be detected at an early preinvasive stage. Thus, a better understanding of the molecular basis of early breast cancer progression is essential. Previously, we discovered that 14-3-3Z is overexpressed in >40% of advanced breast cancers, and this overexpression predicts poor patient survival. Here, we examined at what stage of breast disease 14-3-3Z overexpression occurs, and we found that increased expression of 14-3-3Z begins at atypical ductal hyperplasia, an early stage of breast disease. To determine whether 14-3-3Z overexpression is a decisive early event in breast cancer, we overexpressed 14-3-3Z in MCF10A cells and examined its effect in a three-dimensional culture model. We discovered that 14-3-3Z overexpression severely disrupted the acini architecture resulting in luminal filling. Proper lumen formation is a result of anoikis, apoptosis due to detachment from the basement membrane. We found that 14-3-3Z overexpression conferred resistance to anoikis. Additionally, 14-3-3Z overexpression in MCF10A cells and in mammary epithelial cells (MEC) from 14-3-3Z transgenic mice reduced expression of p53, which is known to mediate anoikis. Mechanistically, 14-3-3Z induced hyperactivation of the phosphoinositide 3-kinase/Akt pathway which led to phosphorylation and translocation of the MDM2 E3 ligase resulting in increased p53 degradation. Ectopic expression of p53 restored luminal apoptosis in 14-3-3Z-overexpressing MCF10A acini in threedimensional cultures. These data suggest that 14-3-3Z overexpression is a critical event in early breast disease, and down-regulation of p53 is one of the mechanisms by which 14-3-3Z alters MEC acini structure and increases the risk of breast cancer. [Cancer Res 2008;68(6):1760-7]