Mitochondria are highly motile organelles that constantly undergo fission and fusion. Impairment of mitochondrial dynamics is associated with mitochondrial dysfunction and is frequently linked to the pathogenesis of neurodegenerative diseases and cancer. We have previously shown that biallelic inactivation of the suppressor of cytokine signaling 6 (SOCS6) gene is a frequent event in human gastric cancer. In this study, we recapitulated the event of SOCS6 loss using a Lentivirus-based knockdown approach, and demonstrated the linkage between SOCS6 depletion and the suppression of programmed cell death. SOCS6 promotes intrinsic apoptosis, with increased Bax conformational change, mitochondrial targeting, and oligomerization. Most importantly, SOCS6 is targeted to mitochondria and induces mitochondrial fragmentation mediated through an increase in DRP1 fission activity. Here, we show that SOCS6 forms complex with DRP1 and the mitochondrial phosphatase PGAM5, attenuates DRP1 phosphorylation, and promotes DRP1 mitochondrial translocation. Based on mutation analyses, SOCS6-mediated apoptosis is tightly coupled to its ability to induce mitochondrial fission. This study demonstrates an important role for SOCS6 in modulating mitochondrial dynamics and apoptosis.

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Vitamin D deficiency has been epidemiologically linked to Alzheimer's disease (AD) and other dementias, but no interventional studies have proved causality. Our previous work revealed that the genomic vitamin D receptor (VDR) is already converted into a non‐genomic signaling pathway by forming a complex with p53 in the AD brain. Here, we extend our previous work to assess whether it is beneficial to supplement AD mice and humans with vitamin D. Intriguingly, we first observed that APP/PS1 mice fed a vitamin D‐sufficient diet showed significantly lower levels of serum vitamin D, suggesting its deficiency may be a consequence not a cause of AD. Moreover, supplementation of vitamin D led to increased Aβ deposition and exacerbated AD. Mechanistically, vitamin D supplementation did not rescue the genomic VDR/RXR complex but instead enhanced the non‐genomic VDR/p53 complex in AD brains. Consistently, our population‐based longitudinal study also showed that dementia‐free older adults (n = 14,648) taking vitamin D3 supplements for over 146 days/year were 1.8 times more likely to develop dementia than those not taking the supplements. Among those with pre‐existing dementia (n = 980), those taking vitamin D3 supplements for over 146 days/year had 2.17 times the risk of mortality than those not taking the supplements. Collectively, these animal model and human cohort studies caution against prolonged use of vitamin D by AD patients.

Identification and functional analysis of genes from genetically altered chromosomal regions would suggest new molecular targets for cancer diagnosis and treatment. Here we performed a genome-wide analysis of chromosomal copy number alterations (CNAs) in matching sets of colon mucosa-adenoma-carcinoma samples using high-throughput oligonucleotide microarray analysis. In silico analysis of NCBI GEO and TCGA datasets allowed us to uncover the significantly altered genes (p ≤ 0.001) associated with the identified CNAs. We performed quantitative PCR analysis of the genomic and complementary DNA derived from primary mucosa, adenoma, and carcinoma samples, and confirmed the recurrent loss and down-regulation of PTPRM in colon adenomas and carcinomas. Functional characterization demonstrated that PTPRM negatively regulates cell growth and colony formation, whereas loss of PTPRM promotes oncogenic cell growth. We further showed that, in accordance to Knudson's two-hit hypothesis, inactivation of PTPRM in colon cancer was mainly attributed to loss of heterozygosity and promoter hypermethylation. Taken together, this study demonstrates a putative tumor suppressive role for PTPRM and that genetic and epigenetic alterations of PTPRM may contribute to early step of colorectal tumorigenesis.

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