BRSK1

BRSK1, also known as SAD-B, is a brain-enriched serine/threonine kinase required for neuronal polarization, with BRSK1/BRSK2 loss disrupting axon-dendrite specification in experimental neurons^[1]. Mechanistically, LKB1 phosphorylates and activates SAD kinases, defining an LKB1-SAD/BRSK pathway required for cortical neuron polarization^[2]. BRSK1 and BRSK2 are activated through phosphorylation of a conserved T-loop threonine, but equivalent ubiquitin-associated-domain mutations produce different effects on BRSK1 and BRSK2 activation, distinguishing the related isoforms^[3]. Downstream polarity control also involves Wee1, because Wee1 persistence in SadA/SadB-deficient neurons disrupts neuronal polarity^[4]. In presynaptic models, SAD-B associates with synaptic vesicles and the active zone cytomatrix, phosphorylates RIM1, and regulates neurotransmitter release^[5]. In breast carcinoma samples and cell lines, cytoplasmic BRSK1 inversely correlates with Jab1, associates with prognosis, and may regulate cell cycle through the PI3K/Akt pathway^[6]. Recent epilepsy genetics further links BRSK1 haploinsufficiency with epilepsy and neurodevelopmental disorders^[7]. For experimental applications, LY294002 increased BRSK1 expression in breast cancer cell-line assays, but direct selective BRSK1 agonist or inhibitor evidence was not retained^[6].- Prioritize BRSK1/BRSK2 comparative designs when testing neuronal polarity mechanisms. - Use pathway-level PI3K/Akt probes only where BRSK1-specific inhibitors remain unsupported.

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