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

P-Rex1 Controls Sphingosine 1-Phosphate Receptor Signalling, Morphology, and Cell-Cycle Progression in Neuronal Cells.
Hampson E, Tsonou E, Baker MJ, Hornigold DC, Hubbard RE, Massey A, Welch HCE

P-Rex1 is a guanine-nucleotide exchange factor (GEF) that activates Rac-type small G proteins in response to the stimulation of a range of receptors, particularly G protein-coupled receptors (GPCRs), to control cytoskeletal dynamics and other Rac-dependent cell responses. P-Rex1 is mainly expressed in leukocytes and neurons. Whereas its roles in leukocytes have been studied extensively, relatively little is known about its functions in neurons. Here, we used CRISPR/Cas9-mediated P-Rex1 deficiency in neuronal PC12 cells that stably overexpress the GPCR S1PR1, a receptor for sphingosine 1-phosphate (S1P), to investigate the role of P-Rex1 in neuronal GPCR signalling and cell responses. We show that P-Rex1 is required for the S1P-stimulated activation of Rac1 and Akt, basal Rac3 activity, and constitutive cAMP production in PC12-S1PR1 cells. The constitutive cAMP production was not due to increased expression levels of major neuronal adenylyl cyclases, suggesting that P-Rex1 may regulate adenylyl cyclase activity. P-Rex1 was required for maintenance of neurite protrusions and spreading in S1P-stimulated PC12-S1PR1 cells, as well as for cell-cycle progression and proliferation. In summary, we identified novel functional roles of P-Rex1 in neuronal Rac, Akt and cAMP signalling, as well as in neuronal cell-cycle progression and proliferation.

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Cells, 10, 9, 18 Sep 2021

PMID: 34572121

Open Access

Optimizing metastatic-cascade-dependent Rac1 targeting in breast cancer: Guidance using optical window intravital FRET imaging.
Floerchinger A, Murphy KJ, Latham SL, Warren SC, McCulloch AT, Lee YK, Stoehr J, Mélénec P, Guaman CS, Metcalf XL, Lee V, Zaratzian A, Da Silva A, Tayao M, Rolo S, Phimmachanh M, Sultani G, McDonald L, Mason SM, Ferrari N, Ooms LM, Johnsson AE, Spence HJ, Olson MF, Machesky LM, Sansom OJ, Morton JP, Mitchell CA, Samuel MS, Croucher DR, Welch HCE, Blyth K, Caldon CE, Herrmann D, Anderson KI, Timpson P, Nobis M

Assessing drug response within live native tissue provides increased fidelity with regards to optimizing efficacy while minimizing off-target effects. Here, using longitudinal intravital imaging of a Rac1-Förster resonance energy transfer (FRET) biosensor mouse coupled with in vivo photoswitching to track intratumoral movement, we help guide treatment scheduling in a live breast cancer setting to impair metastatic progression. We uncover altered Rac1 activity at the center versus invasive border of tumors and demonstrate enhanced Rac1 activity of cells in close proximity to live tumor vasculature using optical window imaging. We further reveal that Rac1 inhibition can enhance tumor cell vulnerability to fluid-flow-induced shear stress and therefore improves overall anti-metastatic response to therapy during transit to secondary sites such as the lung. Collectively, this study demonstrates the utility of single-cell intravital imaging in vivo to demonstrate that Rac1 inhibition can reduce tumor progression and metastases in an autochthonous setting to improve overall survival.

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Cell reports, 36, 11, 14 Sep 2021

PMID: 34525350

The GPCR adaptor protein norbin suppresses the neutrophil-mediated immunity of mice to pneumococcal infection.
Pantarelli C, Pan D, Chetwynd S, Stark AK, Hornigold K, Machin P, Crossland L, Cleary SJ, Baker MJ, Hampson E, Mandel A, Segonds-Pichon A, Walker R, van 't Veer C, Riffo-Vasquez Y, Okkenhaug K, Pitchford S, Welch HCE

Streptococcal pneumonia is a worldwide health problem that kills ∼2 million people each year, particularly young children, the elderly, and immunosuppressed individuals. Alveolar macrophages and neutrophils provide the early innate immune response to clear pneumococcus from infected lungs. However, the level of neutrophil involvement is context dependent, both in humans and in mouse models of the disease, influenced by factors such as bacterial load, age, and coinfections. Here, we show that the G protein-coupled receptor (GPCR) adaptor protein norbin (neurochondrin, NCDN), which was hitherto known as a regulator of neuronal function, is a suppressor of neutrophil-mediated innate immunity. Myeloid norbin deficiency improved the immunity of mice to pneumococcal infection by increasing the involvement of neutrophils in clearing the bacteria, without affecting neutrophil recruitment or causing autoinflammation. It also improved immunity during Escherichia coli-induced septic peritonitis. It increased the responsiveness of neutrophils to a range of stimuli, promoting their ability to kill bacteria in a reactive oxygen species-dependent manner, enhancing degranulation, phagocytosis, and the production of reactive oxygen species and neutrophil extracellular traps, raising the cell surface levels of selected GPCRs, and increasing GPCR-dependent Rac and Erk signaling. The Rac guanine-nucleotide exchange factor Prex1, a known effector of norbin, was dispensable for most of these effects, which suggested that norbin controls additional downstream targets. We identified the Rac guanine-nucleotide exchange factor Vav as one of these effectors. In summary, our study presents the GPCR adaptor protein norbin as an immune suppressor that limits the ability of neutrophils to clear bacterial infections.

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Blood advances, 5, 16, 24 Aug 2021

PMID: 34402884

Open Access