Additional studies are required to determine why some breast cancer cells express relatively high levels of p27(Kip1) despite its known role as an inhibitor of cell cycle progression.
To address this question, here, we transfected the MCF7 breast cancer cell line and the MCF10F nontumorigenic mammary epithelial cell line with a vector containing the p27Kip1 cDNA to obtain derivatives that express increased levels of p27Kip1.
In epithelial cells of normal and benign breast disease, expression of p27Kip1 was well preserved while its expression markedly decreased in breast cancer (45 of 68).
In order to evaluate biological and genetic properties of early breast carcinomas we analyzed microdissected tissue from 33 primary breast carcinomas stage T1b and T1c with respect to the nuclear DNA content, the expression pattern of Ki-67, cyclin A, p27KIP1, p53 and p21WAF1, and chromosomal gains and losses.
Previously, immunochemical analysis of a series of breast cancer cell lines demonstrated a correlation between the expression of p27(Kip1) and the breast cancer susceptibility gene BRCA1.
Thus, cytoplasmic relocalization of p27(kip1), secondary to Akt-mediated phosphorylation, is a novel mechanism whereby the growth inhibitory properties of p27(kip1) are functionally inactivated and the proliferation of breast cancer cells is sustained.
High p27Kip1 expression was an independent predictor of responsiveness to hormonal therapy and thus may be useful for the selection of premenopausal women with early-stage hormone receptor-positive breast cancer for adjuvant combination endocrine therapy.
The purpose is to evaluate expression levels of Jun activation domain-binding protein 1 (JAB1) in breast cancer tissue and adjacent normal tissue, to determine whether JAB1 expression is associated with p27(Kip1) expression in invasive breast carcinomas, and to evaluate the prognostic significance of JAB1 and p27(Kip1) in node-negative breast cancer.
These data suggest that agents that up-regulate p27(Kip1) or inhibit growth factor signaling via the extracellular signal-regulated kinases should be tested as therapeutic strategies in tamoxifen-resistant breast cancer.
In conclusion, expression levels of p21Waf1, p27Kip1, p53 and cyclin D3 significantly increased after preoperative chemotherapy in breast carcinomas but only high Ki-67 expression, negative estrogen receptor status and negative progesterone receptor status were associated with complete pathologic response to preoperative chemotherapy.
In a parsimonious multivariable proportional hazards model, protein levels of cyclin E, p27(Kip1), p53, and the presence of glomeruloid microvascular proliferation all independently predicted outcome after breast cancer.
The cyclin-dependent kinase inhibitor p27 (Kip1) is an important cell cycle regulatory gene in breast cancer, and decreased p27 expression is associated with poor prognosis.
Elevated levels of the cell cycle protein cyclin E, and low levels of its inhibitor, p27(Kip1), have been associated with a poor prognosis following breast cancer.
Furthermore, we identified high expression of FOXA1 in breast cancer cell lines and tissues, discovered a role for BRCA1 in the regulation of p27(Kip1) transcription and a possible interaction with BRCA1.
Although the exact biological mechanism remains to be explored, our findings suggest possible involvement of CDKN1A and CDKN1B variants in the etiology of breast cancer.