Mutations in the clathrin-assembly gene Picalm are responsible for the hematopoietic and iron metabolism abnormalities in fit1 mice

Abstract

Recessive N-ethyl-N-nitrosourea (ENU)-induced mutations recovered at the fitness-1 (fit1) locus in mouse chromosome 7 cause hematopoietic abnormalities, growth retardation, and shortened life span, with varying severity of the defects in different alleles. Abnormal iron distribution and metabolism and frequent scoliosis have also been associated with an allele of intermediate severity (fit1 4R ). We report that fit1 4R , as well as the most severe fit1 5R allele, are nonsense point mutations in the mouse ortholog of the human phosphatidylinositol-binding clathrin assembly protein (PICALM) gene, whose product is involved in clathrin-mediated endocytosis. A variety of leukemias and lymphomas have been associated with translocations that fuse human PICALM with the putative transcription factor gene AF10. The Picalm fit1-5R and Picalm fit1-4R mutations are splice-donor alterations resulting in transcripts that are less abundant than normal and missing exons 4 and 17, respectively. These exon deletions introduce premature termination codons predicted to truncate the proteins near the N and C termini, respectively. No mutations in the genes encoding Picalm, clathrin, or components of the adaptor protein complex 2 (AP2) have been previously described in which the suite of disorders present in the Picalm fit1 mutant mice is apparent. These mutants thus provide unique models for exploring how the endocytic function of mouse Picalm and the transport processes mediated by clathrin and the AP2 complex contribute to normal hematopoiesis, iron metabolism, and growth.

The role of CALM–AF10 gene fusion in acute leukemia

“…12 These domains include the epsin N-terminal homology (ENTH) domain (Asp-Pro-Phe), a DPF (ASP-Pro-Phe) motif, an NPF (Asn-Pro-Phe) motif and type I and II clathrin-binding sequences (CBS I and II). [13][14][15] The predicted CALM protein is similar to the neuronal specific monomeric clathrin assembly protein AP180, which was first identified in coated vesicles of bovine brain. 16,17 CALM homologues have been identified in rat, mouse and cow.…”

“…23 Finally, point mutations in the CALM gene led to ineffective hematopoiesis, functional iron deficiency and altered growth in mice, suggesting that CALM may play a role in endocytosis-mediated iron transport. 15 In addition to an established role in endocytosis, a recent study suggested that CALM may interact with nuclear proteins. 24 In this study, the novel protein CATS (CALM interacting protein, expressed in thymus and spleen) was shown to interact with a region of the CALM protein that is retained in the CALM-AF10 fusion protein and increased the nuclear localization of both CALM and a CALM-AF10 fusion protein.…”

P2‐030: Investigating the Role of Clu, Picalm, and Cr1 in Alzheimer's Disease

“…Klebig et al reported fit1 mice, with mutations in PICALM, showed a decreased lifespan and growth retardation, along with numerous haematopoietic abnormalities, manifesting in severe anaemia and a decreased white blood cell count (Klebig et al 2003), suggesting potential roles for PICALM in growth, haematopoiesis and iron metabolism. There are a number of different fit1 mice, each with a different mutation within PICALM, and with phenotypic severity related to the severity of the mutations (Klebig et al 2003).…”

“…There are a number of different fit1 mice, each with a different mutation within PICALM, and with phenotypic severity related to the severity of the mutations (Klebig et al 2003). …”

“…If PICALM is a major player in determining the endocytosis of VAMP2, as appears to be the case, genetic changes which alter its function or regulation could affect VAMP2, interfering with normal neurotransmitter release, disruption of which could result in failed communication between neurons, leading to issues with learning and memory, as are seen in AD (Yao 2004). The strongest phenotype in Fit1 mice is seen when there are nonsense mutations in PICALM's ANTH domain -the very domain underlying its interaction with the SNARE proteins (Klebig et al 2003), perhaps indicative that it is the disruption of the PICALM/VAMP2 interaction that so disrupts normal development and function (Miller et al 2011). Synaptic dysfunction could also underlie the observed relationship between PICALM and cognitive ability (Mengel-From et al 2010).…”