Mark E. Burkard

I. Using chemical genetics to understand how protein kinases control cell divisionSource: Lera & Burkard, Molecules, 2012

Polo-like kinase 1 (Plk1) is a central regulator of human cell division (mitosis) and its function is important to maintain genomic integrity. Moreover, Plk1 is a target of emerging cancer therapies. Understanding how Plk1 functions in mitosis is a major challenge. First, it catalyzes hundreds of phosphorylation events. Second, Plk1’s roles in early mitosis often prevent analysis of later events using classic loss-of-function approaches. To overcome these limitations, we have developed a general set of chemical genetic tools and discovered Plk1 function at the inner KT and in cytokinesis. Our analog sensitive Plk1 technology allows us to separate Plk1 function by subcompartment. Our ultimate goal is to understand how the hundreds of Plk1 substrates mediate its mitotic functions. This promises to finally reveal the unknown phosphorylation events mediating well-known functions of Plk1. This toolbox can be repurposed to interrogate mechanism of any signaling enzyme.

To identify how Plk1 is functioning along the kinetochore-centromere axis, we fused Plk1 to various components along this axis and performed phosphoproteomic analysis in collaboration with Professor Joshua Coon’s Research Group. We observed distinct phosphoproteomic and functional roles, suggesting that Plk1 exists and functions in discrete pools along this axis.

Source: Lera et al, Nat Chem Bio, 2016

II. Precision Medicine

1. Identifying Vulnerabilities of Cancer

A. Polyploidy/Aneuploidy
A high percentage of cancer cells have gains of losses of whole chromosomes (aneuploidy) or whole sets of chromosomes (polyploidy). Polyploidy is associated with higher risk We are trying to learn more about ways to specifically target polyploid cells to better treat cancers. We recently identified DBPQ and 8-azaguanine as polyploid-selective compounds, as shown below.

Source: Choudhary et al, Mol Cancer Ther, 2016

B. Centrosome Amplification
Centrosome amplification is a hallmark of cancer cells, predicts worse outcomes in human cancer patients, and leads to error-prone mitotic cell divisions. We are trying to learn more about the causes and consequences of centrosome amplification in cancer with the goal of identifying novel pathways to target to better treat cancers with centrosome amplification.

2. Identifying biomarkers to better target our current therapeutics

Breast cancer patients are routinely treated with combination chemotherapy, but we know that some patients do not benefit from receiving one or more of these therapies. However, it is currently impossible to predict which patients will benefit. As chemotherapy involves risks and has side effects, it is of great importance to identify biomarkers for these therapies. The lab is particularly interested in learning why certain patients respond to paclitaxel, a commonly used cancer therapy. Contrary to long-held belief, we (in collaboration with Dr. Beth Weaver’s Lab) have shown that mitotic arrest is not required for a clinical response to paclitaxel. Furthermore, paclitaxel may be exerting its clinical activity by inducing multipolar spindles, as shown  here.

Source: Zasadil et al, Sci Trans Med, 2014