Life Sciences Research for Lifelong Health

Heidi Welch

Research Summary

We study molecular mechanisms that control the Rac protein family, which regulates cell shape, cell movement, oxygen radical formation and gene expression. In particular, we study the proteins that activate Rac, so-called Rac-GEFs. A few years ago, we discovered a new type of Rac-GEF, the P-Rex family, and we have been studying the mechanisms that regulate their activity and their functional roles.

We found that P-Rex family Rac-GEFs are important for the ability of our white blood cells to defend us against bacterial and fungal infections, for the shape and electrical functions of nerve cells that control the coordination of our movements, and for the distribution of skin pigment cells during development. We also participated in studies which showed that the deregulation of the cellular amount or activity of P-Rex family Rac-GEFs contribute to cancer growth and metastasis.

Currently, our lab is investigating new functional roles of P-Rex and other Rac-GEFs, particularly in inflammatory cells, and we are inventing new ways of monitoring Rac-GEF activity.

Latest Publications

Platelets in neutrophil recruitment to sites of inflammation.
Pitchford S, Pan D, Welch HC

This review describes the essential roles of platelets in neutrophil recruitment from the bloodstream into inflamed and infected tissues, with a focus on recent findings.

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Current opinion in hematology, , 1531-7048, , 2016

PMID: 27820736

Truncating PREX2 mutations activate its GEF activity and alter gene expression regulation in NRAS-mutant melanoma.
Lissanu Deribe Y, Shi Y, Rai K, Nezi L, Amin SB, Wu CC, Akdemir KC, Mahdavi M, Peng Q, Chang QE, Hornigold K, Arold ST, Welch HC, Garraway LA, Chin L

PREX2 (phosphatidylinositol-3,4,5-triphosphate-dependent Rac-exchange factor 2) is a PTEN (phosphatase and tensin homolog deleted on chromosome 10) binding protein that is significantly mutated in cutaneous melanoma and pancreatic ductal adenocarcinoma. Here, genetic and biochemical analyses were conducted to elucidate the nature and mechanistic basis of PREX2 mutation in melanoma development. By generating an inducible transgenic mouse model we showed an oncogenic role for a truncating PREX2 mutation (PREX2(E824)*) in vivo in the context of mutant NRAS. Using integrative cross-species gene expression analysis, we identified deregulated cell cycle and cytoskeleton organization as significantly perturbed biological pathways in PREX2 mutant tumors. Mechanistically, truncation of PREX2 activated its Rac1 guanine nucleotide exchange factor activity, abolished binding to PTEN and activated the PI3K (phosphatidyl inositol 3 kinase)/Akt signaling pathway. We further showed that PREX2 truncating mutations or PTEN deletion induces down-regulation of the tumor suppressor and cell cycle regulator CDKN1C (also known as p57(KIP2)). This down-regulation occurs, at least partially, through DNA hypomethylation of a differentially methylated region in chromosome 11 that is a known regulatory region for expression of the CDKN1C gene. Together, these findings identify PREX2 as a mediator of NRAS-mutant melanoma development that acts through the PI3K/PTEN/Akt pathway to regulate gene expression of a cell cycle regulator.

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Proceedings of the National Academy of Sciences of the United States of America, , 1091-6490, , 2016

PMID: 26884185

Norbin Stimulates the Catalytic Activity and Plasma Membrane Localization of the Guanine-Nucleotide Exchange Factor P-Rex1.
Pan D, Barber MA, Hornigold K, Baker MJ, Toth JM, Oxley D, Welch HC

P-Rex1 is a guanine-nucleotide exchange factor (GEF) that activates the small G protein (GTPase) Rac1 to control Rac1-dependent cytoskeletal dynamics, and thus cell morphology. Three mechanisms of P-Rex1 regulation are currently known: (i) binding of the phosphoinositide second messenger PIP3, (ii) binding of the Gβγ subunits of heterotrimeric G proteins, and (iii) phosphorylation of various serine residues. Using recombinant P-Rex1 protein to search for new binding partners, we isolated the G-protein coupled receptor (GPCR)-adaptor protein Norbin (Neurochondrin, NCDN) from mouse brain fractions. Coimmunoprecipitation confirmed the interaction between overexpressed P-Rex1 and Norbin in COS-7 cells, as well as between endogenous P-Rex1 and Norbin in HEK-293 cells. Binding assays with purified recombinant proteins showed that their interaction is direct, and mutational analysis revealed that the PH domain of P-Rex1 is required. Rac-GEF activity assays with purified recombinant proteins showed that direct interaction with Norbin increases the basal, PIP3- and Gβγ-stimulated Rac-GEF activity of P-Rex1. Pak-CRIB pull-down assays demonstrated that Norbin promotes the P-Rex1 mediated activation of endogenous Rac1 upon stimulation of HEK-293 cells with lysophosphatidic acid. Finally, immunofluorescence microscopy and subcellular fractionation showed that coexpression of P-Rex1 and Norbin induces a robust translocation of both proteins from the cytosol to the plasma membrane, as well as promoting cell spreading, lamellipodia formation and membrane ruffling, cell morphologies generated by active Rac1. In summary, we have identified a novel mechanism of P-Rex1 regulation through the GPCR-adaptor protein Norbin, a direct P-Rex1 interacting protein that promotes the Rac-GEF activity and membrane localization of P-Rex1.

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The Journal of biological chemistry, , 1083-351X, , 2016

PMID: 26792863

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Keywords

cell adhesion
gtpases
immunity
inflammation
migration
signalling

Group Members

Latest Publications

Platelets in neutrophil recruitment to sites of inflammation.

Pitchford S, Pan D, Welch HC

Current opinion in hematology
1531-7048: (2016)

PMID: 27820736

Truncating PREX2 mutations activate its GEF activity and alter gene expression regulation in NRAS-mutant melanoma.

Lissanu Deribe Y, Shi Y, Rai K

Proceedings of the National Academy of Sciences of the United States of America
1091-6490: (2016)

PMID: 26884185

Norbin Stimulates the Catalytic Activity and Plasma Membrane Localization of the Guanine-Nucleotide Exchange Factor P-Rex1.

Pan D, Barber MA, Hornigold K

The Journal of biological chemistry
1083-351X: (2016)

PMID: 26792863

Small GTPases and their guanine-nucleotide exchange factors and GTPase-activating proteins in neutrophil recruitment.

Baker MJ, Pan D, Welch HC

Current opinion in hematology
23 1531-7048:44-54 (2016)

PMID: 26619317

Regulation and Function of P-Rex Family Rac-GEFs.

Welch HC

Small GTPases
2154-1256:0 (2015)

PMID: 25961466

P-Rex and Vav Rac-GEFs in platelets control leukocyte recruitment to sites of inflammation.

Pan D, Amison RT, Riffo-Vasquez Y

Blood
1528-0020: (2014)

PMID: 25538043

A rac1-independent role for p-rex1 in melanoblasts.

Lindsay CR, Li A, Faller W

The Journal of investigative dermatology
135 1523-1747:314-8 (2015)

PMID: 25075639