Stk38 interactomics by proximity ligation

STK38 (aka NDR1) is a Hippo pathway serine/threonine protein kinase with multifarious functions in normal and cancer cells. Using a context-dependent proximity labelling assay, we discovered that STK38 modulates its interaction with more than 250 proteins depending on the context. Upon starvation-induced autophagy, STK38 associates with cytoplasmic proteins while upon ECM detachment it binds to mainly nuclear proteins. This differential subcellular-localization-dependent activity is caused by the XPO1 (Exportin-1, CRM1) dependent nuclear/cytoplasmic shuttling of STK38. STK38 associates with nuclear related partners upon ECM detachment and with cytoplasmic related ones upon autophagy, exhibiting a nuclear/cytoplasmic shuttling under the dependency of XPO1 (Exportin-1, aka CRM1). We further uncovered that the XPO1-mediated export of STK38 is dependent on phosphorylation of XPO1s serin residue 1055 by STK38 itself. In addition to regulating its own nuclear export, STK38 also controls the subcellular distribution of Beclin1, a key regulator of autophagy. Moreover, the regulation of XPO1 by STK38 mediates the nuclear exclusion of YAP1. Collectively, our results reveal that functions of STK38 are linked to the XPO1-mediated subcellular distribution of STK38 and key regulators. These observations show that unrelated cellular functions can be regulated by a same mechanism controlled by a single kinase and demonstrate a novel mechanism of XPO1-dependent cargo export regulation y phosphorylation of XPO1s C-terminal auto-inhibitory domain.