{"type": "root", "children": [{"type": "p", "children": [{"type": "t", "text": "\n Inositol polyphosphate‐5‐phosphatase E (INPP5E) is a 72‐kDa enzyme that regulates the phosphoinositide composition of membranes by hydrolyzing the 5‑phosphate from substrates such as phosphatidylinositol (3,4,5)‐trisphosphate and phosphatidylinositol (4,5)‐bisphosphate. This activity is critical for maintaining proper phosphoinositide ratios in specialized membrane regions, most notably within the primary cilium, where INPP5E helps to modulate signal transduction pathways.\n "}]}, {"type": "t", "text": "\n "}, {"type": "p", "children": [{"type": "t", "text": "\n Mutations in INPP5E have been linked to ciliopathies such as Joubert syndrome, with defective INPP5E activity leading to instability and premature disassembly of cilia."}, {"type": "fg", "children": [{"type": "fg_fs", "start_ref": "1", "end_ref": "3"}]}, {"type": "t", "text": " INPP5E is targeted to the ciliary membrane through a C‑terminal motif that requires binding to prenyl‐binding proteins (e.g. PDE6D) and is further facilitated by ciliary factors such as ARL13B and TULP3, which ensure its proper localization and function within the primary cilium."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "2"}, {"type": "fg_f", "ref": "4"}]}, {"type": "t", "text": " Moreover, finely tuned INPP5E activity at the centrosome and ciliary base is essential for initiating ciliogenesis; by modulating phosphatidylinositol 4‑phosphate levels, INPP5E regulates the recruitment of tau‑tubulin kinase and the removal of inhibitory capping proteins, processes that are critical for axoneme elongation and ciliary assembly."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "5"}]}, {"type": "t", "text": "\n "}]}, {"type": "t", "text": "\n "}, {"type": "p", "children": [{"type": "t", "text": "\n Beyond its role in ciliary biology, INPP5E has emerging functions in the regulation of intracellular trafficking and signal transduction. In neuronal cells, for example, part of the INPP5E pool localizes to lysosomes where its enzymatic activity is required for efficient autophagosome–lysosome fusion, thereby influencing autophagic flux and neuronal homeostasis."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "7"}]}, {"type": "t", "text": " Additionally, phosphorylation of INPP5E by Aurora kinase A has been shown to enhance its 5‑phosphatase activity, creating a feedback loop that modulates ciliary disassembly and links INPP5E activity to cell cycle and signal regulatory events."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "9"}]}, {"type": "t", "text": "\n "}]}, {"type": "t", "text": "\n "}, {"type": "p", "children": [{"type": "t", "text": "\n INPP5E also plays roles in developmental and disease contexts. In the neural tube, for instance, appropriate expression of INPP5E is required for normal embryonic neurodevelopment, and reduced levels have been associated with neural tube defects."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "10"}]}, {"type": "t", "text": " In the retina, INPP5E is enriched in the inner segment and connecting cilium of photoreceptors, and its loss leads to retinal degeneration, highlighting its tissue‐specific functions."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "12"}]}, {"type": "t", "text": " Furthermore, modulation of INPP5E levels by microRNAs (e.g. miR‑598) has been implicated in colon cancer cell proliferation, and negative regulation of the IGF‑1/PI3K/Akt pathway by INPP5E (also known as pharbin) underscores its broader impact on cell signaling cascades."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "13"}]}, {"type": "t", "text": "\n "}]}, {"type": "t", "text": "\n "}, {"type": "p", "children": [{"type": "t", "text": "\n Collectively, these studies reveal that INPP5E is a multifaceted regulator of phosphoinositide signaling whose precise localization to cilia and lysosomes is essential for ciliogenesis, autophagy, and diverse signaling pathways. Disruption of INPP5E activity leads to defects in ciliary stability, developmental anomalies, and disease, emphasizing its critical role in maintaining cellular function."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "1"}, {"type": "fg_f", "ref": "7"}, {"type": "fg_f", "ref": "9"}, {"type": "fg_f", "ref": "5"}, {"type": "fg_f", "ref": "4"}, {"type": "fg_fs", "start_ref": "11", "end_ref": "14"}, {"type": "fg_f", "ref": "10"}, {"type": "fg_f", "ref": "3"}, {"type": "fg_f", "ref": "6"}, {"type": "fg_f", "ref": "8"}]}, {"type": "t", "text": "\n "}]}, {"type": "rg", "children": [{"type": "r", "ref": 1, "children": [{"type": "t", "text": "Stephanie L Bielas, Jennifer L Silhavy, Francesco Brancati, et al. 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