WELCOME TO THE NARLA LAB
The Narla Lab is part of the Division of Genetic Medicine in the Department of Internal Medicine at the University of Michigan's Rogel Cancer Center
THE NARLA LAB
Our lab is interested in understanding the molecular processes that underlie the genesis and progression of human tumors. Our current and future work is directed towards the following three interconnected areas: 1) the functional characterization of physiologic and cancer-related post translational regulation of PP2A, 2) identifying the biological and structural basis for the evolutionary selection and fitness of cancer-derived mutations of PP2A and, 3) the development and characterization of small molecule activators of PP2A (SMAPs) as both chemical tools to probe PP2A regulation and for the treatment of PP2A dependent diseases. The Narla lab is located at the Rogel Cancer Center at the University of Michigan within the Division of Genetic Medicine.
Protein phosphatases are vital molecular switches that balance many cellular processes through the reversible de-phosphorylation of key signaling proteins. Protein Phosphatase 2A (PP2A) is a serine/threonine phosphatase that regulates many oncogenic signaling pathways, thereby biologically functioning as a tumor suppressor. The structure of PP2A is a trimeric holoenzyme composed of a catalytic subunit C, a scaffolding subunit A, and one of many different regulatory subunits B, which dictate PP2A substrate specificity and intracellular localization. The A scaffolding subunit is composed of 15 tandem HEAT (Huntington Elongation A subunit Tor) repeats that provide the protein tremendous flexibility, enabling the production of a diverse repertoire of B subunit dependent holoenzymes capable of dephosphorylating targeted substrates. While it is one of the most abundant cellular proteins, PP2A is dysregulated and deactivated in cancer by the numerous mechanisms somatic mutations, increased expression of endogenous PP2A inhibitors, epigenetic silencing, and post-translational modifications of various subunits. Overexpression of endogenous inhibitors of PP2A, such as SET and CIP2A, have been associated with tumor progression and poor prognosis in cancer.
Where achievable, restoration of PP2A function inhibits cancer progression, and notably, by a mediator that is downstream of the oncogenic kinases that initiate and drive cancer progression. While several therapeutics have been developed to indirectly target PP2A, studies have uncovered small molecules such as phenothiazines that directly activate PP2A. Nevertheless, because their pronounced extrapyramidal and anti-cholinergic effects were severely dose limiting, further pursuit of phenothiazines and related dibenzazepines for treatment of cancer seems unlikely. To explore the full potential of antipsychotics as anticancer agents, we reengineered the tricyclic neuroleptics to decouple the CNS pharmacology from the anti-proliferative properties of this drug class. Iterative rounds of synthesis and optimization lead to the development of a class of small molecule activators of PP2A (SMAPs).
SMAP treatment of KRAS-mutant lung cancer cell lines induced apoptosis and decreased the phosphorylation of PP2A targets such a pERK. Xenograft and transgenic mouse models of KRAS-mutant lung cancer further demonstrated the therapeutic potential of SMAP therapy through SMAP dependent inhibition of tumor growth. Molecular analysis of these tumors showed induction of apoptosis and dephosphorylation of targets of PP2A. Biochemical studies showed that SMAPs bound to the PP2A-A subunit and induced a conformational change in PP2A. PP2A was further confirmed as the primary target of these small molecules as mutation of putative binding sites and PP2A dysregulation by SV40 small T expression inhibited the anti-tumorigenic potential of SMAP therapy in cellular and xenograft models. This work was published and featured in the Journal of Clinical Investigation.
07 / 17 / 2018