The positive correlation between ATG and DCTPP
The positive correlation between ATG7 and DCTPP1 (TCGA data) suggested our hypothesis that DCTPP1 may affect the phenotype of prostate tumor, or maybe other types of tumors as well, through its role in autophagy. To test this hypothesis, we carried out western-blot experiments in which the ratios of LC3-II and β-actin (housekeeping gene) were calculated and used for monitoring autophagy activity in different cell types. Lysosomal turnover of the autophagosomal marker LC3-II reflects starvation-induced autophagic activity, therefore detection of LC3 by immunoblotting or immunofluorescence has been commonly used for monitoring autophagy and autophagy-related processes . The western-blot results showed that overexpression of DCTPP1 was always associated with high level of LC3-II/β-actin ratio in in vitro and in vivo, indicating an enhanced autophagy activity. We also counted the numbers of autophagosomes in vitro through TEM, which also indicated that overexpression of DCTPP1 associated with autophagy level in vitro.
To support our hypothesis, we carried out the following bioinformatics analyses. The results of PPI analysis suggested that Cytokine-induced apoptosis inhibitor 1 (CIAPIN1) is closely related to DCTPP1. CIAPIN1, an important player in tumor angiogenesis and division, has been reported as a prognostic factor in multiple cancers, such as hepatocrcinoma, breast carcinoma, thyroid carcinoma and colon cancer etc. . Studies have shown that CIAPIN1 possibly regulates apoptosis through a new route, bypassing the classical cell-intrinsic or cell-extrinsic pathways which involves genes in Bcl-2 family and caspase family [, , ]. Apoptosis and autophagy are two cellular activities which play antagonistic roles to determine the fate of a cell, and they have been heatedly discussed in the literature . The positive correlation between DCTPP1 and CIAPIN1 in our study (TCGA data) suggested that increased expression of CIAPIN1 may suppress apoptosis activity, resulting in enhanced autophagy activity which is associated with the increased expression level of DCTPP1. Indeed, the observed change in cell density is the result of a combined effect of cell proliferation and cell death. In our study, the L-α-Aminoadipic Acid assays did not show any significant difference between the DCTPP1 overexpression group and control group (data not shown). Thus, we conclude that the observed increase in cell density may be mainly explained by the reduced apoptosis which is the consequence of the activation in autophagy due to the overexpression of DCTPP1.
The results of KEGG pathway analysis suggested that DCTPP1 and AKT serine/threonine kinase 3 (AKT3) should be negatively associated within PI3K/AKT/mTOR pathway that regulates autophagy, which was consistent with the TCGA data. AKT3 is the third homology of the Akt/PKB family, which encodes serine/threonine kinases, a key member of PI3K/AKT/mTOR pathway [, , ]. When PI3K/AKT/mTOR pathway is activated, DCTPP1 will be downregulated and autophagy activity will be suppressed, and vice versa. Nevertheless, it was unexpected that LST8 homolog (MLST8), a MTOR associated protein, which is a compound of mTORC1 complex  was positively correlated with DCTPP1 but negatively correlated with AKT3. We believe upstream AKT3 gene may play a more important and broader role than downstream MLST8 gene in dictating PI3K/AKT/mTOR pathway which influences autophagy. Further research is needed to uncover the underlying relatedness between DCTPP1 and genes which are involved in various steps of PI3K/AKT/mTOR pathway, and their functions in prostate cancer cells.
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Introduction Global genome sequencing efforts have revealed millions of genes encoding unknown proteins for which there is no direct experimental proof of function (Galperin and Koonin, 2004, Hanson et al., 2010, Osterman and Overbeek, 2003, Roberts, 2004). “Unknown” and “hypothetical” proteins represent a large fraction (30% to 50%) of the genes in sequenced genomes and metagenomes, limiting our knowledge of these organisms and biology in general. Maf-like proteins constitute a large family of conserved unknown sequences found in bacteria, archaea, and eukaryotes (over 7,300 sequences in databases; Pfam PF02545 and IPR003697). The name Maf (for multicopy associated filamentation) was proposed in a previous genetic work, which demonstrated that the introduction of maf on a multicopy plasmid into Bacillus subtilis cells resulted in an inhibition of septation and extensive filamentation of cells (Butler et al., 1993). However, the inactivation of maf did not produce any apparent phenotype in B. subtilis cells, indicating that it is not required for cell division (Butler et al., 1993). The B. subtilis Maf protein is homologous to the Escherichia coli YhdE (previous name, OrfE; 46% sequence identity), and on the chromosome, both genes are associated with the shape-determining genes mreBCD. The morphogenetic complex MreBCD is responsible for the maintenance of rod cell morphology, and the E. coli MreB is also involved in chromosome segregation and nucleoid separation (Butler et al., 1993, Kruse et al., 2005, Wachi et al., 1991).