Inhibiting the m6A Reader IGF2BP3 Suppresses Ovarian Cancer Cell Growth via Regulating PLAGL2 mRNA Stabilization.

Background: The oncogene IGF2 mRNA binding protein 3 (IGF2BP3) could function as an m6A reader in stabilizing many tumor-associated genes' mRNAs. However, the relevant oncogenic mechanism by which IGF2BP3 promotes ovarian cancer growth is largely unknown. Methods: The IGF2BP3 expression in ovarian cancer was identified by retrieving the datasets from The Cancer Genome Atlas (TCGA). GEO datasets evaluated the relevant signaling pathways in IGF2BP3 knockdown in ovarian cancer cells. IGF2BP3 positive correlation gene in TCGA was calculated. MTS proliferation assay was identified in IGF2BP3 knockdown and rescued by PLAG1 like zinc finger 2 (PLAGL2) overexpression in ES-2 and SKOV3 cells. Bioinformatic analysis and RIP-qPCR were predicted and identified the IGF2BP3 binding site and PLAGL2 mRNA stability. The animal experiment identified IGF2BP3 proliferation inhibition. Results: IGF2BP3 was upregulated in ovarian cancer tissue and cells. The depletion of IGF2BP3 in ovarian cancer cells leads to an enhancement of the pathway involved in cellular proliferation and mRNA stability. IGF2BP3 positive correlation suppressed pro-proliferation gene PLAGL2. IGF2BP3 knockdown suppressed ovarian cancer cell proliferation and was rescued by PLAGL2 overexpression. Luciferase reporter assay confirmed that IGF2BP3 could bind to 3'-UTR of PLAGL2 to maintain the mRNA stability. Further, in in vivo experiments, IGF2BP3 knockdown suppressed ovarian cancer cell proliferation via inhibiting PLAGL2 expression. Conclusion: All of these indicate that PLAGL2 mediates the main function of IGF2BP3 knockdown on ovarian cancer proliferation inhibition through mRNA stability regulation.

Specific regions of the SulA protein recognized and degraded by the ATP-dependent ClpYQ (HslUV) protease in Escherichia coli.

In Escherichia coli, ClpYQ (HslUV) is a two-component ATP-dependent protease, in which ClpQ is the peptidase subunit and ClpY is the ATPase and unfoldase. ClpY functions to recognize protein substrates, and denature and translocate the unfolded polypeptides into the proteolytic site of ClpQ for degradation. However, it is not clear how the natural substrates are recognized by the ClpYQ protease and the mechanism by which the substrates are selected, unfolded and translocated by ClpY into the interior site of ClpQ hexamers. Both Lon and ClpYQ proteases can degrade SulA, a cell division inhibitor, in bacterial cells. In this study, using yeast two-hybrid and in vivo degradation analyses, we first demonstrated that the C-terminal internal hydrophobic region (139th∼149th aa) of SulA is necessary for binding and degradation by ClpYQ. A conserved region, GFIMRP, between 142th and 147th residues of SulA, were identified among various Gram-negative bacteria. By using MBP-SulA(F143Y) (phenylalanine substituted with tyrosine) as a substrate, our results showed that this conserved residue of SulA is necessary for recognition and degradation by ClpYQ. Supporting these data, MBP-SulA(F143Y), MBP-SulA(F143N) (phenylalanine substituted with asparagine) led to a longer half-life with ClpYQ protease in vivo. In contrast, MBP-SulA(F143D) and MBP-SulA(F143S) both have shorter half-lives. Therefore, in the E. coli ClpYQ protease complex, ClpY recognizes the C-terminal region of SulA, and F143 of SulA plays an important role for the recognition and degradation by ClpYQ protease.

The degradation of RcsA by ClpYQ(HslUV) protease in Escherichia coli.

In Escherichia coli, RcsA, a positive activator for transcription of cps (capsular polysaccharide synthesis) genes, is degraded by the Lon protease. In lon mutant, the accumulation of RcsA leads to overexpression of capsular polysaccharide. In a previous study, overproduction of ClpYQ(HslUV) protease represses the expression of cpsB∷lacZ, but there has been no direct observation demonstrating that ClpYQ degrades RcsA. By means of a MBP-RcsA fusion protein, we showed that RcsA activated cpsB∷lacZ expression and could be rapidly degraded by Lon protease in SG22622 (lon(+)). Subsequently, the comparative half-life experiments performed in the bacterial strains SG22623 (lon) and AC3112 (lon clpY clpQ) indicated that the RcsA turnover rate in AC3112 was relatively slow and RcsA was stable at 30°C or 41°C. In addition, ClpY could interact with RscA in an in vitro pull-down assay, and the more rapid degradation of RcsA was observed in the presence of ClpYQ protease at 41°C. Thus, we conclude that RcsA is indeed proteolized by ClpYQ protease.

Stepwise activity of ClpY (HslU) mutants in the processive degradation of Escherichia coli ClpYQ (HslUV) protease substrates.

In Escherichia coli, ClpYQ (HslUV) is a two-component ATP-dependent protease composed of ClpY (HslU), an ATPase with unfolding activity, and ClpQ (HslV), a peptidase. In the ClpYQ proteolytic complex, the hexameric rings of ClpY (HslU) are responsible for protein recognition, unfolding, and translocation into the proteolytic inner chamber of the dodecameric ClpQ (HslV). Each of the three domains, N, I, and C, in ClpY has its own distinct activity. The double loops (amino acids [aa] 137 to 150 and 175 to 209) in domain I of ClpY are necessary for initial recognition/tethering of natural substrates such as SulA, a cell division inhibitor protein. The highly conserved sequence GYVG (aa 90 to 93) pore I site, along with the GESSG pore II site (aa 265 to 269), contribute to the central pore of ClpY in domain N. These two central loops of ClpY are in the center of its hexameric ring in which the energy of ATP hydrolysis allows substrate translocation and then degradation by ClpQ. However, no data have been obtained to determine the effect of the central loops on substrate binding or as part of the processivity of the ClpYQ complex. Thus, we probed the features of ClpY important for substrate engagement and protease processivity via random PCR or site-specific mutagenesis. In yeast two-hybrid analysis and pulldown assays, using isolated ClpY mutants and the pore I or pore II site of ClpY, each was examined for its influence on the adjoining structural regions of the substrates. The pore I site is essential for the translocation of the engaged substrates. Our in vivo study of the ClpY mutants also revealed that an ATP-binding site in domain N, separate from its role in polypeptide (ClpY) oligomerization, is required for complex formation with ClpQ. Additionally, we found that the tyrosine residue at position 408 in ClpY is critical for stabilization of hexamer formation between subunits. Therefore, our studies suggest that stepwise activities of the ClpYQ protease are necessary to facilitate the processive degradation of its natural substrates.