{"type": "root", "children": [{"type": "p", "children": [{"type": "t", "text": "\nPurkinje cell protein 4 (PCP4), also known as PEP‐19, is a small, intrinsically disordered calmodulin‐binding protein that modulates Ca²⁺–calmodulin signaling by markedly accelerating both calcium ion association and dissociation. Such modulation is achieved in part through its acidic domain that can bind Ca²⁺ directly, thereby tuning the kinetics of CaM‐dependent processes. In the nervous system, PCP4 is expressed in a highly specific pattern—most prominently in cerebellar Purkinje cells and in select neuronal populations within the neocortex, hippocampus, and olfactory regions—where it regulates intracellular calcium dynamics that are critical for neuronal differentiation and survival. In transgenic and neuroblastoma cell models, altered PCP4 levels have been shown to affect the timing of neuronal maturation and to function as a negative regulator of neurite outgrowth, emphasizing its importance in fine‐tuning neurodevelopmental processes."}, {"type": "fg", "children": [{"type": "fg_fs", "start_ref": "1", "end_ref": "6"}]}, {"type": "t", "text": "\n"}]}, {"type": "t", "text": "\n\n"}, {"type": "p", "children": [{"type": "t", "text": "\nOutside the central nervous system, emerging evidence implicates PCP4 in the regulation of endocrine functions and in the pathobiology of cancer. In the adrenal cortex, PCP4 is predominantly expressed in the aldosterone‐producing zona glomerulosa and within aldosterone‐producing adenomas, where it modulates CaM‐dependent signaling pathways that control aldosterone synthesis. In parallel, in human breast cancer cell lines, PCP4/PEP19 exhibits anti‐apoptotic functions and influences cell adhesion, migration, and invasion—processes that are intimately linked to the epithelial–mesenchymal transition and tumor progression—thereby making it a potential oncotarget irrespective of estrogen receptor status."}, {"type": "fg", "children": [{"type": "fg_fs", "start_ref": "7", "end_ref": "9"}]}, {"type": "t", "text": "\n"}]}, {"type": "t", "text": "\n\n"}, {"type": "p", "children": [{"type": "t", "text": "\nFurthermore, recent studies have expanded the functional repertoire of PCP4 by linking its dysregulation to altered differentiation processes and neurodevelopmental disorders. For instance, a circular RNA–mediated mechanism that targets PCP4 has been shown to affect osteogenic differentiation and osteogenesis‐coupled angiogenesis in bone marrow mesenchymal stem cells, suggesting roles in skeletal homeostasis. Moreover, the gene’s location on human chromosome 21 and its overexpression in Down syndrome models have been associated with precocious neuronal differentiation and aberrant CaMKII activation, offering a potential mechanistic connection to the Alzheimer’s disease neuropathology observed in Down syndrome patients."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "10"}]}, {"type": "t", "text": "\n"}]}, {"type": "rg", "children": [{"type": "r", "ref": 1, "children": [{"type": "t", "text": "John A Putkey, Quinn Kleerekoper, Tara R Gaertner, et al. 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"}, {"type": "b", "children": [{"type": "t", "text": "The calmodulin regulator protein, PEP-19, sensitizes ATP-induced Ca2+ release."}]}, {"type": "t", "text": " "}, {"type": "i", "children": [{"type": "t", "text": "J Biol Chem (2013)"}]}, {"type": "t", "text": " DOI: "}, {"type": "a", "children": [{"type": "t", "text": "10.1074/jbc.M112.411314"}], "href": "https://doi.org/10.1074/jbc.M112.411314"}, {"type": "t", "text": " PMID: "}, {"type": "a", "children": [{"type": "t", "text": "23204517"}], "href": "https://pubmed.ncbi.nlm.nih.gov/23204517"}]}, {"type": "r", "ref": 4, "children": [{"type": "t", "text": "François Mouton-Liger, Ignasi Sahún, Thibault Collin, et al. "}, {"type": "b", "children": [{"type": "t", "text": "Developmental molecular and functional cerebellar alterations induced by PCP4/PEP19 overexpression: implications for Down syndrome."}]}, {"type": "t", "text": " "}, {"type": "i", "children": [{"type": "t", "text": "Neurobiol Dis (2014)"}]}, {"type": "t", "text": " DOI: "}, {"type": "a", "children": [{"type": "t", "text": "10.1016/j.nbd.2013.11.016"}], "href": "https://doi.org/10.1016/j.nbd.2013.11.016"}, {"type": "t", "text": " PMID: "}, {"type": "a", "children": [{"type": "t", "text": "24291518"}], "href": "https://pubmed.ncbi.nlm.nih.gov/24291518"}]}, {"type": "r", "ref": 5, "children": [{"type": "t", "text": "Maria Renelt, Viola von Bohlen und Halbach, Oliver von Bohlen und Halbach "}, {"type": "b", "children": [{"type": "t", "text": "Distribution of PCP4 protein in the forebrain of adult mice."}]}, {"type": "t", "text": " "}, {"type": "i", "children": [{"type": "t", "text": "Acta Histochem (2014)"}]}, {"type": "t", "text": " DOI: "}, {"type": "a", "children": [{"type": "t", "text": "10.1016/j.acthis.2014.04.012"}], "href": "https://doi.org/10.1016/j.acthis.2014.04.012"}, {"type": "t", "text": " PMID: "}, {"type": "a", "children": [{"type": "t", "text": "24954028"}], "href": "https://pubmed.ncbi.nlm.nih.gov/24954028"}]}, {"type": "r", "ref": 6, "children": [{"type": "t", "text": "Ikumi Kitazono, Taiji Hamada, Takuya Yoshimura, et al. "}, {"type": "b", "children": [{"type": "t", "text": "PCP4/PEP19 downregulates neurite outgrowth via transcriptional regulation of Ascl1 and NeuroD1 expression in human neuroblastoma M17 cells."}]}, {"type": "t", "text": " "}, {"type": "i", "children": [{"type": "t", "text": "Lab Invest (2020)"}]}, {"type": "t", "text": " DOI: "}, {"type": "a", "children": [{"type": "t", "text": "10.1038/s41374-020-0462-z"}], "href": "https://doi.org/10.1038/s41374-020-0462-z"}, {"type": "t", "text": " PMID: "}, {"type": "a", "children": [{"type": "t", "text": "32641824"}], "href": "https://pubmed.ncbi.nlm.nih.gov/32641824"}]}, {"type": "r", "ref": 7, "children": [{"type": "t", "text": "Saulo J A Felizola, Yasuhiro Nakamura, Yoshikiyo Ono, et al. 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