Class III phosphatidylinositol-3-OH kinase controls epithelial integrity through endosomal LKB1 regulation

Abstract

The molecular mechanisms underlying the interdependence between intracellular trafficking and epithelial cell polarity are poorly understood. Here we show that inactivation of class III phosphatidylinositol-3-OH kinase (CIII-PI3K), which produces phosphatidylinositol-3-phosphate (PtdIns3P) on endosomes, disrupts epithelial organization. This is caused by dysregulation of endosomally localized Liver Kinase B1 (LKB1, also known as STK11), which shows delocalized and increased activity accompanied by dysplasia-like growth and invasive behaviour of cells provoked by JNK pathway activation. CIII-PI3K inactivation cooperates with Ras to promote tumour growth in vivo in an LKB1-dependent manner. Strikingly, co-depletion of LKB1 reverts these phenotypes and restores epithelial integrity. The endosomal, but not autophagic, function of CIII-PI3K controls polarity. We identify the CIII-PI3K effector, WD repeat and FYVE domain-containing 2 (WDFY2), as an LKB1 regulator in Drosophila tissues and human organoids. Thus, we define a CIII-PI3K-regulated endosomal signalling platform from which LKB1 directs epithelial polarity, the dysregulation of which endows LKB1 with tumour-promoting properties.

PI3K isoforms in cell signalling and vesicle trafficking

“…Another kinase regulated by Vps34 is the endosomally-localized pool of LKB1 kinase, an activator of AMPK and a regulator of cell polarity 221 . This polarity function of LKB1 depends on its binding to the endosomally-localised WDFY2, a FYVE domain-containing protein, and the transit of LKB1 from Rab5to Rab7-positive compartments during endosomal maturation.…”

Class III PI3K Vps34 Controls Thyroid Hormone Production by Regulating Thyroglobulin Iodination, Lysosomal Proteolysis, and Tissue Homeostasis

“…We favor instead the hypothesis of TSHR mistrafficking into intracellular vesicles. Recent work in Drosophila revealed that Vps34 inactivation or pharmacological inhibition using the small molecule inhibitor SAR405 causes alteration of cell polarity and disruption of epithelial architecture by relieving LKB1 inhibition and triggering JNK activation (14). A role of Vps34 in epithelial organization and polarity was also observed in 3D cultures of Caco-2 kidney cells (14).…”

“…Recent work in Drosophila revealed that Vps34 inactivation or pharmacological inhibition using the small molecule inhibitor SAR405 causes alteration of cell polarity and disruption of epithelial architecture by relieving LKB1 inhibition and triggering JNK activation (14). A role of Vps34 in epithelial organization and polarity was also observed in 3D cultures of Caco-2 kidney cells (14). It would be interesting to analyze the activation states of LKB1 and JNK in Vps34 cKO thyroid tissue, and, if modified, to cross Vps34 cKO with floxed LKB1 alleles.…”

“…Vps34/PIK3C3 (also referred to as type III PI 3-kinase) has long been recognized as a main actor involved in the general control of endocytic vesicular trafficking (8)(9)(10)(11)(12)(13). Vps34/PIK3C3 also plays an important role in epithelial organization in Drosophila (14) and in autophagy (12,15), both in the initiation of autophagosome formation and in the progression toward autophagosome-lysosome fusion (16,17).…”

IRSp53 shapes the plasma membrane and controls polarized transport at the nascent lumen during epithelial morphogenesis

“…4A, B). We performed a similar experiment also in IRSp53-KO Caco-2 cells by monitoring the distribution of aPKC, which is the most commonly-used apical marker in this in for the distribution of aPKC 28,30,31 . Likewise in MDCK cells, IRSp53 depletion resulted in formation of aPKC multi-foci at the 3-4-cell stage during cystogenesis, as compared to the control Caco-2 cells ( Supplementary Fig.…”