Humanin binds MPP8: mapping interaction sites of the peptide and protein

Mitochondrial-derived peptides: Antidiabetic functions and evolutionary perspectives

Mitochondrial-derived peptides (MDPs) are a novel class of bioactive microproteins encoded by short open-reading frames (sORF) in mitochondrial DNA (mtDNA). Currently, three types of MDPs have been identified: Humanin (HN), MOTS-c (Mitochondrial ORF within Twelve S rRNA type-c), and SHLP1-6 (small Humanin-like peptide, 1 to 6). The 12 S ribosomal RNA (MT-RNR1) gene harbors the sequence for MOTS-c, whereas HN and SHLP1-6 are encoded by the 16 S ribosomal RNA (MT-RNR2) gene. Special genetic codes are used in mtDNA as compared to nuclear DNA: (i) ATA and ATT are used as start codons in addition to the standard start codon ATG; (ii) AGA and AGG are used as stop codons instead of coding for arginine; (iii) the standard stop codon UGA is used to code for tryptophan. While HN, SHLP6, and MOTS-c are encoded by the H (heavy owing to high guanine + thymine base composition)-strand of the mtDNA, SHLP1-5 are encoded by the L (light owing to less guanine + thymine base composition)-strand. MDPs attenuate disease pathology including Type 1 diabetes (T1D), Type 2 diabetes (T2D), gestational diabetes, Alzheimer's disease (AD), cardiovascular diseases, prostate cancer, and macular degeneration. The current review will focus on the MDP regulation of T2D, T1D, and gestational diabetes along with an emphasis on the evolutionary pressures for conservation of the amino acid sequences of MDPs.

MPP8 Promotes Proliferation and Restrains Apoptosis in Osteosarcoma by Regulating p38αMAPK Pathway

Osteosarcoma is the most common primary bone malignancy. We aim to investigate that role of M-phase phosphoprotein 8 (MPP8) on proliferation and apoptosis in osteosarcoma. Briefly, the current research reported an in vitro study investigating the role MPP8 in OS tumorigenesis. Consequently, we found that the MPP8 expression was upregulated in osteosarcoma tissues and in osteosarcoma cell lines. Interestingly, MPP8 knockdown via shRNA restrained the cell viability and proliferation of U2OS and Saos-2 cells. In addition, MPP8 knockdown promoted the apoptosis of U2OS and Saos-2 cells, while MPP8 overexpression promotes proliferation and inhibited the cell apoptosis of osteosarcoma cells. These results suggested that MPP8 may serve as a contributor for osteosarcoma growth and inhibition of MPP8 may help restrain the development of osteosarcoma. Importantly, we found that MPP8 overexpression suppressed the protein levels of HOXA5, p38αMAPK, increased cell proliferation and inhibited cell apoptosis, while co-transfection with HOXA5 overexpression suppressed the cell proliferation and increased cell apoptosis. These results indicated that MPP8 contributed to cell proliferation and the underlying mechanism might be involved with HOXA5/ p38αMAPK pathway.

Lentivirus-mediated knockdown of M-phase phosphoprotein 8 inhibits proliferation of colon cancer cells

M-phase phosphoprotein 8 (MPP8) has been reported to be overexpressed in various human carcinoma cells and was associated with tumor malignant characters. However, its functional role in colon cancer (CRC) is still unclear. In the present study, lentivirus-mediated short hairpin RNAs were designed to silence the MPP8 gene in CRC cells including RKO and SW1116 cells. The fluorescence microscopy was used to determine the knockdown efficiency of MPP8 by observing lentivirus-mediated green fluorescent protein expression. MPP8 expression in infected RKO and SW1116 was evaluated by real-time PCR and Western blot analysis. Cell proliferation was assessed by MTT assay and colony formation. Flow cytometry was applied to measure cell cycle and apoptosis. Transwell assay was used to determine the effect of MMP8 silencing on cell migration. Our results demonstrated that loss of MPP8 inhibited cell proliferation and migration and promoted cell apoptosis. These results indicate that MPP8 plays an important role in the proliferation and metastasis of CRC cells and suggest that silencing of MPP8 may be an effective therapeutic approach for the treatment of CRC.

Humanin: Functional Interfaces with IGF-I

Humanin is the first newly discovered peptide encoded in the mitochondrial genome in over three decades. It is the first member of a novel class of mitochondrial derived peptides. This small, 24 amino acid peptide was initially discovered to have neuroprotective effects and subsequent experiments have shown that it is beneficial in a diverse number of disease models including stroke, cardiovascular disease, and cancer. Over a decade ago, our lab found that humanin bound IGFBP-3 and more recent studies have found it to decrease circulating IGF-I levels. In turn, IGF-I also seems to regulate humanin levels and in this review, we cover the known interaction between humanin and IGF-I. Although the exact mechanism for how humanin and IGF-I regulate each other still needs to be elucidated, it is clear that humanin is a new player in IGF-I signaling.

Humanin and age-related diseases: a new link?

Humanin (HN) is 24-amino acid mitochondria-associated peptide. Since its initial discovery over a decade ago, a role for HN has been reported in many biological processes such as apoptosis, cell survival, substrate metabolism, inflammatory response, and response to stressors such as oxidative stress, ischemia, and starvation. HN and its potent analogs have been shown to have beneficial effects in many age-related diseases including Alzheimer's disease, stroke, diabetes, myocardial ischemia and reperfusion, atherosclerosis, amyotrophic lateral sclerosis, and certain types of cancer both in vitro and in vivo. More recently, an association between HN levels, growth hormone/insulin-like growth factor-1 (GH/IGF axis), and life span was demonstrated using various mouse models with mutations in the GH/IGF axis. The goal of this review is to summarize the current understanding of the role of HN in aging and age-related diseases.