Functional Ablation of pRb Activates Cdk2 and Causes Antiestrogen Resistance in Human Breast Cancer Cells

Estrogens are required for the proliferation of hormone dependent breast cancer cells, making estrogen receptor (ER) positive tumors amenable to endocrine therapies such as antiestrogens. However, resistance to these agents remains a significant cause of treatment failure. We previously demonstrated that inactivation of the retinoblastoma protein (pRb) family tumor suppressors causes antiestrogen resistance in MCF-7 cells, a widely studied model of estrogen responsive human breast cancers. In this study, we investigate the mechanism by which pRb inactivation leads to antiestrogen resistance. Cdk4 and cdk2 are two key cell cycle regulators that can phosphorylate and inactivate pRb, therefore we tested whether these kinases are required in cells lacking pRb function. pRb family members were inactivated in MCF-7 cells by expressing polyomavirus large tumor antigen (PyLT), and cdk activity was inhibited using the cdk inhibitors p16INK4A and p21Waf1/Cip1. Cdk4 activity was no longer required in cells lacking functional pRb, while cdk2 activity was required for proliferation in both the presence and absence of pRb function. Using inducible PyLT cell lines, we further demonstrated that pRb inactivation leads to increased cyclin A expression, cdk2 activation and proliferation in antiestrogen arrested cells. These results demonstrate that antiestrogens do not inhibit cdk2 activity or proliferation of MCF-7 cells in the absence of pRb family function, and suggest that antiestrogen resistant breast cancer cells resulting from pRb pathway inactivation would be susceptible to therapies that target cdk2

Doxorubicin Increases Mitochondrial DNA Copy Number in Human Breast Cancer Cells

Mitochondria are dynamic organelles with important functions in energy production, biosynthesis, and regulation of cell death. Mitochondrial DNA (mtDNA) copy number is the ratio of mtDNA relative to nuclear DNA [1] and is a measure of mitochondrial capacity. Using mtDNA copy number measurements, we can measure an increase or decrease in mitochondrial capacity as a response to different drug treatments. Doxorubicin is a chemotherapy drug that works by disrupting DNA’s structure [2]. It is widely used in the treatment of breast cancer, however recurrence of disease after doxorubicin treatment is a major clinical problem. A greater understanding of doxorubicin’s effects could identify biomarkers that would predict drug resistance or new therapeutic interventions that would decrease the likelihood of resistance. In previous studies, we showed that doxorubicin resistant breast cancer cells have increased mtDNA copy number [3]. We recently showed that mtDNA copy number expansion mediates the ‘survivability’ of doxorubicin exposure in yeast [4]. In the current study, we show breast cancer cells exposed to a dose of doxorubicin that is not acutely cytotoxic respond by increasing their mtDNA copy number. This response is shared by cell lines that represent the four major clinical subtypes of breast cancer. The expansion of mtDNA could represent a remodeling of metabolism to facilitate cell cycle arrest that allows cells to evade cytotoxicity. Alternatively, it could represent a compensation to mitochondrial injury. Future experiments will explore these possibilities.University of Minnesota's Undergraduate Research Opportunities Progra

Development of an interdisciplinary pre-matriculation program designed to promote medical students’ self efficacy

Background and objectives: A four-week interdisciplinary pre-matriculation program for Native American and rural medical students was created and its impact on students’ transition to medical school was assessed. The program extends the goals of many pre-matriculation programs by aiming to increase not only students’ understanding of basic science knowledge, but also to build student self-efficacy through practice with medical school curricular elements while developing their academic support networks. Design: A mixed method evaluation was used to determine whether the goals of the program were achieved (n = 22). Student knowledge gains and retention of the microbiology content were assessed using a microbiology concept inventory. Students participated in focus groups to identify the benefits of participating in the program as well as the key components of the program that benefitted the students. Results: Program participants showed retention of microbiology content and increased confidence about the overall medical school experience after participating in the summer program. Conclusions: By nurturing self-efficacy, participation in a pre-matriculation program supported medical students from Native American and rural backgrounds during their transition to medical school. Abbreviations: CAIMH: Center of American Indian and Minority Health; MCAT: Medical College Admission Test; PBL: Problem based learning; UM MSD: University of Minnesota Medical School Dulut