LAUSR

Significance Proteins are modified by many posttranslational modifications (PTMs) with crucial regulatory functions. A PTM attracting increasing interest is ADP-ribosylation, capable of altering crucial cellular targets. We show that mono-ADP-ribosylation by PARP12 of the protein Golgin-97 regulates transport to the plasma membrane of a specific group of functionally crucial cargo proteins. PARP12 is shown to be part of a regulatory cascade initiated by PKD and involving the direct phosphorylation and activation of PARP12. These events define, through Golgin-97 mono-ADP-ribosylation, a Golgi sorting mechanism for specific basolateral cargoes, including E-cadherin. Defects in this cascade impair E-cadherin transport and formation of cell–cell contacts, with potential consequences for the formation of adherens junctions, polarization of epithelial cells, and development of epithelial–mesenchymal transformation. Adenosine diphosphate (ADP)-ribosylation is a posttranslational modification involved in key regulatory events catalyzed by ADP-ribosyltransferases (ARTs). Substrate identification and localization of the mono-ADP-ribosyltransferase PARP12 at the trans-Golgi network (TGN) hinted at the involvement of ARTs in intracellular traffic. We find that Golgin-97, a TGN protein required for the formation and transport of a specific class of basolateral cargoes (e.g., E-cadherin and vesicular stomatitis virus G protein [VSVG]), is a PARP12 substrate. PARP12 targets an acidic cluster in the Golgin-97 coiled-coil domain essential for function. Its mutation or PARP12 depletion, delays E-cadherin and VSVG export and leads to a defect in carrier fission, hence in transport, with consequent accumulation of cargoes in a trans-Golgi/Rab11–positive intermediate compartment. In contrast, PARP12 does not control the Golgin-245–dependent traffic of cargoes such as tumor necrosis factor alpha (TNFα). Thus, the transport of different basolateral proteins to the plasma membrane is differentially regulated by Golgin-97 mono-ADP-ribosylation by PARP12. This identifies a selective regulatory mechanism acting on the transport of Golgin-97– vs. Golgin-245–dependent cargoes. Of note, PARP12 enzymatic activity, and consequently Golgin-97 mono-ADP-ribosylation, depends on the activation of protein kinase D (PKD) at the TGN during traffic. PARP12 is directly phosphorylated by PKD, and this is essential to stimulate PARP12 catalytic activity. PARP12 is therefore a component of the PKD-driven regulatory cascade that selectively controls a major branch of the basolateral transport pathway. We propose that through this mechanism, PARP12 contributes to the maintenance of E-cadherin–mediated cell polarity and cell–cell junctions.