Kalirin, a large, multi-domain Rho GDP/GTP exchange factor (GEF), is expressed both within and outside of the nervous system. Genetic studies revealed roles for human KALRN in early onset coronary artery disease, schizophrenia, Alzheimer disease and attention deficit hyperactivity disorder. The use of several promoters and alternative splicing generate multiple isoforms of Kalirin. Studies to date have focused on Kal7, the major isoform in the adult brain, revealing an essential role for its ability to activate Rac1 n dendritic spine formation and function. Kal9 and Kal12, the major isoforms expressed outside of the nervous system, include a second Rho GEF domain specific for RhoA. Mice unable to produce any of the major isoforms of Kalirin (KalSRKO) share the deficits observed in Kal7KO mice and exhibit an array of additional deficits. Most prominent is their stunted growth, impaired maternal behavior, reduced atherosclerosis, diminished trabecular and cortical bone mass and impaired neuromuscular junction formation. We first identified Kalirin based on its interaction with an essential secretory granule membrane enzyme, peptidylglycine ?-amidating monooxygenase (PAM). Our analysis of KalSRKO mice and expression of Kalirin in a corticotrope cell line support the hypothesis that Kalirin plays a crucial role in the ability of peptide secreting cells to adjust their secretory pathway to environmental inputs such as growth factors and extracellular matrix components.
In Aim 1, we will use corticotrope tumor cells as our bioassay system for understanding how the Sec14 domain of Kalirin affects secretion and endocytic trafficking. Using a FRET biosensor for activated Rac1, we will relate Rac1 activation to exocytosis. Key findings will be tested using primary pituitary cultures from wildtype and KalSRKO mice.
In Aim 2, we will use a structural approach to build towards understanding how the presence of a Sec14 domain, multiple spectrin repeats and a Rho GEF in a single protein is used to accomplish the precise spatial and temporal control needed to regulate membrane trafficking. Purified recombinant Sec14, spectrin repeat regions and Kal7 will be characterized with in vitro assays and used for crystallographic studies. Secreted peptides and proteins have widespread modulatory effects on cell growth and differentiation. A better understanding of the mechanisms by which Kalirin conveys signals to the pathways through which basal and regulated secretion occur will offer specific targets for intervention and control of secretion.

Public Health Relevance

Endocrine cells and neurons secrete peptides and proteins to adjust target tissue function in response to changes in the environment. The studies proposed focus on the roles of one specific protein in this process; human genetic studies, along with our analysis of mice lacking the gene encoding this protein, support its role in controlling secretion. A better basic understanding of this process and the proteins involved will offer specific targets for intervention and control of secretion.

National Institute of Health (NIH)
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Research Project (R01)
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Molecular and Cellular Endocrinology Study Section (MCE)
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Malozowski, Saul N
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University of Connecticut
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Mains, Richard E; Blaby-Haas, Crysten; Rheaume, Bruce A et al. (2018) Changes in Corticotrope Gene Expression Upon Increased Expression of Peptidylglycine ?-Amidating Monooxygenase. Endocrinology 159:2621-2639
Miller, Megan B; Yan, Yan; Wu, Yi et al. (2017) Alternate promoter usage generates two subpopulations of the neuronal RhoGEF Kalirin-7. J Neurochem 140:889-902
Miller, Megan B; Yan, Yan; Machida, Kazuya et al. (2017) Brain Region and Isoform-Specific Phosphorylation Alters Kalirin SH2 Domain Interaction Sites and Calpain Sensitivity. ACS Chem Neurosci 8:1554-1569
Katrancha, Sara M; Wu, Yi; Zhu, Minsheng et al. (2017) Neurodevelopmental disease-associated de novo mutations and rare sequence variants affect TRIO GDP/GTP exchange factor activity. Hum Mol Genet 26:4728-4740
Kumar, Dhivya; Mains, Richard E; Eipper, Betty A (2016) 60 YEARS OF POMC: From POMC and ?-MSH to PAM, molecular oxygen, copper, and vitamin C. J Mol Endocrinol 56:T63-76
Yan, Yan; Eipper, Betty A; Mains, Richard E (2016) Kalirin is required for BDNF-TrkB stimulated neurite outgrowth and branching. Neuropharmacology 107:227-238
Lu, Jianning; Luo, Ceng; Bali, Kiran Kumar et al. (2015) A role for Kalirin-7 in nociceptive sensitization via activity-dependent modulation of spinal synapses. Nat Commun 6:6820
Puigdellívol, Mar; Cherubini, Marta; Brito, Verónica et al. (2015) A role for Kalirin-7 in corticostriatal synaptic dysfunction in Huntington's disease. Hum Mol Genet 24:7265-85
Miller, Megan B; Vishwanatha, Kurutihalli S; Mains, Richard E et al. (2015) An N-terminal Amphipathic Helix Binds Phosphoinositides and Enhances Kalirin Sec14 Domain-mediated Membrane Interactions. J Biol Chem 290:13541-55
Yan, Yan; Eipper, Betty A; Mains, Richard E (2015) Kalirin-9 and Kalirin-12 Play Essential Roles in Dendritic Outgrowth and Branching. Cereb Cortex 25:3487-501

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