Date of Award

2021

Document Type

Dissertation

Degree Name

Philosophy (Ph.D)

Department

Biological Sciences

First Advisor

Zhu Yan

Second Advisor

Yong Yu

Third Advisor

Matteo Ruggiu

Abstract

Zinc deficiency has been linked to human diseases including cancer. p53, a zinc-containing transcription factor, is the most frequently mutated tumor suppressor protein in human cancer. MDM2 and MDMX are zinc- containing proteins and crucial negative regulators of p53, which have been found to be amplified or overexpressed in various cancers. To investigate the effects of zinc depletion on the p53 signaling pathway, we have used ion chelators TPEN and bispicen as well as zinc-deficient medium to treat cells. We report here that zinc depletion results in MDMX degradation in a ubiquitination-independent and 20S proteasome-dependent manner. Restoration of zinc recovers the cellular levels of MDMX. Further, TPEN treatment inhibits growth of the MCF-7 cells, a breast cancer cell line that remains wild type p53, which is partially rescued by over- expression of MDMX. Moreover, we identified TRPM7, a zinc-permeable ion channel, as a novel MDMX- interacting protein. TRPM7 stabilizes and induces ectopic MDMX migration changes on SDS-PAGE. Depletion of TRPM7 attenuates while TRPM7 overexpression facilitates the recovery of MDMX upon adding back zinc to TPEN-treated cells. Importantly, we found that TRPM7 inhibition, like TPEN treatment, decreases breast cancer cell MCF-7 proliferation and migration. The inhibitory effect on cell migration upon TRPM7 inhibition is also partially rescued by over-expression of MDMX. Together, our data indicate that TRPM7 regulates cellular levels of MDMX in part by modulating the intracellular Zn2+ concentration to promote tumorigenesis.

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