The molecular mechanisms underlying the formation of carriers trafficking from the Golgi complex to the cell surface are still ill-defined; nevertheless, the involvement of a lipid-based machinery is well established. This includes phosphatidylinositol 4-phosphate (PtdIns(4)P), the precursor for phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P(2)). In yeast, PtdIns(4)P exerts a direct role, however, its mechanism of action and its targets in mammalian cells remain uncharacterized. We have identified two effectors of PtdIns(4)P, the four-phosphate-adaptor protein 1 and 2 (FAPP1 and FAPP2). Both proteins localize to the trans-Golgi network (TGN) on nascent carriers, and interact with PtdIns(4)P and the small GTPase ADP-ribosylation factor (ARF) through their plekstrin homology (PH) domain. Displacement or knockdown of FAPPs inhibits cargo transfer to the plasma membrane. Moreover, overexpression of FAPP-PH impairs carrier fission. Therefore, FAPPs are essential components of a PtdIns(4)P- and ARF-regulated machinery that controls generation of constitutive post-Golgi carriers.

Oculocerebrorenal syndrome of Lowe is caused by mutation of OCRL1, a phosphatidylinositol 4,5-bisphosphate 5-phosphatase localized at the Golgi apparatus. The cellular role of OCRL1 is unknown, and consequently the mechanism by which loss of OCRL1 function leads to disease is ill defined. Here, we show that OCRL1 is associated with clathrin-coated transport intermediates operating between the trans-Golgi network (TGN) and endosomes. OCRL1 interacts directly with clathrin heavy chain and promotes clathrin assembly in vitro. Interaction with clathrin is not, however, required for membrane association of OCRL1. Overexpression of OCRL1 results in redistribution of clathrin and the cation-independent mannose 6-phosphate receptor (CI-MPR) to enlarged endosomal structures that are defective in retrograde trafficking to the TGN. Depletion of cellular OCRL1 also causes partial redistribution of a CI-MPR reporter to early endosomes. These findings suggest a role for OCRL1 in clathrin-mediated trafficking of proteins from endosomes to the TGN and that defects in this pathway might contribute to the Lowe syndrome phenotype.

Digital health technology tools (DHTTs) present real opportunities for accelerating innovation, improving patient care, reducing clinical trial duration and minimising risk in medicines development. This review is comprised of four case studies of DHTTs used throughout the lifecycle of medicinal products, starting from their development. These cases illustrate how the regulatory requirements of DHTTs used in medicines development are based on two European regulatory frameworks (medical device and the medicinal product regulations) and highlight the need for increased collaboration between various stakeholders, including regulators (medicines regulators and device bodies), pharmaceutical sponsors, manufacturers of devices and software, and academia. As illustrated in the examples, the complexity of the interactions is further increased by unique challenges related to DHTTs. These case studies are the main examples of DHTTs with a regulatory assessment thus far, providing an insight into the applicable current regulatory approach; they were selected by a group of authors, including regulatory specialists from pharmaceutical sponsors, technology experts, academic researchers and employees of the European Medicines Agency. For each case study, the challenges faced by sponsors and proposed potential solutions are discussed, and the benefit of a structured interaction among the different stakeholders is also highlighted.