Abemaciclib-induced epithelial-mesenchymal transition mediated by cyclin-dependent kinase 4/6 independent of cell cycle arrest pathway.

Abemaciclib (ABM), a cyclin-dependent kinase 4/6 inhibitor, shows pharmacological effects in cell cycle arrest. Epithelial-mesenchymal transition is an important cellular event associated with pathophysiological states such as organ fibrosis and cancer progression. In the present study, we evaluated the contribution of factors associated with cell cycle arrest to ABM-induced epithelial-mesenchymal transition. Treatment with 0.6 µM ABM induced both cell cycle arrest and epithelial-mesenchymal transition-related phenotypic changes. Interestingly, the knockdown of cyclin-dependent kinase 4/6, pharmacological targets of ABM or cyclin D1, which forms complexes with cyclin-dependent kinase 4/6, resulted in cell cycle arrest at the G1-phase and induction of epithelial-mesenchymal transition, indicating that downregulation of cyclin-dependent kinase 4/6-cyclin D1 complexes would mimic ABM. In contrast, knockdown of the Rb protein, which is phosphorylated by cyclin-dependent kinase 4/6, had no effect on the expression level of α-smooth muscle actin, an epithelial-mesenchymal transition marker. Furthermore, ABM-induced epithelial-mesenchymal transition was not affected by Rb knockdown, suggesting that Rb is not involved in the transition process. Our study is the first to suggest that cyclin-dependent kinase 4/6-cyclin D1 complexes, as pharmacological targets of ABM, may contribute to ABM-induced epithelial-mesenchymal transition, followed by clinical disorders such as organ fibrosis and cancer progression. This study suggests that blocking epithelial-mesenchymal transition might be a promising way to prevent negative side effects caused by a medication (ABM) without affecting its ability to treat the disease.

Transporter Protein Expression of Corneal Epithelium in Rabbit and Porcine: Evaluation of Models for Ocular Drug Transport Study.

The transcorneal route is the main entry route for drugs to the intraocular parts, after topical administration. The outer surface, the corneal epithelium (CE), forms the rate-limiting barrier for drug permeability. Information about the role and protein expression of drug and amino acid transporter proteins in the CE is sparse and lacking. The aim of our study was to characterize transporter protein expression in rabbit and porcine CE to better understand potential drug and nutrient absorption after topical administration. Proteins, mainly Abc and Slc transporters, were characterized with quantitative targeted absolute proteomics and global untargeted proteomics methods. In the rabbit CE, 24 of 48 proteins were detected in the targeted approach, and 21 of these were quantified. In the porcine CE, 26 of 58 proteins were detected in the targeted approach, and 20 of these were quantified. Among these, 15 proteins were quantified in both animals: 4f2hc (Slc3a2), Aqp0, Asct1 (Slc1a4), Asct2 (Slc1a5), Glut1 (Slc2a1), Hmit (Slc2a13), Insr, Lat1 (Slc7a5), Mct1 (Slc16a1), Mct2 (Slc16a7), Mct4 (Slc16a3), Mrp 4 (Abcc4), Na+/K+-ATPase, Oatp3a1 (Slco3a1), and Snat2 (Slc38a2). Overall, the global proteomics results supported the targeted proteomics results. Organic anion transporting polypeptide Oatp3a1 was detected and quantified for the first time in both rabbit (1.4 ± 0.4 fmol/cm2) and porcine (11.1 ± 5.3 fmol/cm2) CE. High expression levels were observed for L-type amino acid transporter, Lat1, which was quantified with newly selected extracellular domain peptides in rabbit (48.9 ± 11.8 fmol/cm2) and porcine (37.6 ± 11.5 fmol/cm2) CE. The knowledge of transporter protein expression in ocular barriers is a key factor in the successful design of new ocular drugs, pharmacokinetic modeling, understanding ocular diseases, and the translation to human.

ZNT5-6 and ZNT7 play an integral role in protein N-glycosylation by supplying Zn2+ to Golgi α-mannosidase II.

The stepwise addition of monosaccharides to N-glycans attached to client proteins to generate a repertoire of mature proteins involves a concerted action of many glycosidases and glycosyltransferases. Here, we report that Golgi α-mannosidase II (GMII), a pivotal enzyme catalyzing the first step in the conversion of hybrid- to complex-type N-glycans, is activated by Zn2+ supplied by the early secretory compartment-resident ZNT5-ZNT6 heterodimers (ZNT5-6) and ZNT7 homodimers (ZNT7). Loss of ZNT5-6 and ZNT7 function results in marked accumulation of hybrid-type and complex/hybrid glycans with concomitant reduction of complex- and high-mannose-type glycans. In cells lacking the ZNT5-6 and ZNT7 functions, the GMII activity is substantially decreased. In contrast, the activity of its homolog, lysosomal mannosidase (LAMAN), is not decreased. Moreover, we show that the growth of pancreatic cancer MIA PaCa-2 cells lacking ZNT5-6 and ZNT7 is significantly decreased in a nude mouse xenograft model. Our results indicate the integral roles of ZNT5-6 and ZNT7 in N-glycosylation and highlight their potential as novel target proteins for cancer therapy.

The Effects of N-Glycosylation on the Expression and Transport Activity of OATP1A2 and OATP2B1.

Organic anion transporting polypeptide (OATP)1A2 and OATP2B1 have potential N-glycosylation sites, but their influence remains unclear. This study aimed to identify the N-glycosylation sites of OATP1A2/2B1 and investigate their impact on the expression and function of OATP1A2/2B1. Human embryonic kidney cells expressing OATP1A2 or OATP2B1 (HEK293-OATP1A2/2B1) were exposed to tunicamycin, an N-glycosylation inhibitor, and a plasma membrane fraction (PMF) Western blot assay and an estrone 3-sulfate (E3S) uptake study were conducted. HEK293-OATP1A2/OATP2B1 cell lines with mutation(s) at potential N-glycosylation sites were established, and the Western blotting and uptake study were repeated. Tunicamycin reduced the PMF levels and E3S uptake of OATP1A2/OATP2B1. The Asn124Gln, Asn135Gln, and Asn492Gln mutations in OATP1A2 and Asn176Gln and Asn538Gln mutations in OATP2B1 reduced the molecular weights of the OATP molecules and their PMF levels. The PMF levels of OATP1A2 Asn124/135Gln, OATP1A2 Asn124/135/492Gln, and OATP2B1 Asn176/538Gln were further reduced. The maximum transport velocities of OATP1A2 Asn124Gln, OATP1A2 Asn135Gln, and OATP2B1 Asn176/538Gln were markedly reduced to 10 %, 4 %, and 10 % of the wild-type level, respectively. In conclusion, the N-glycans at Asn124 and Asn135 of OATP1A2 and those at Asn176 and Asn538 of OATP2B1 are essential for the plasma membrane expression of these molecules and also affect their transport function.

Aggregability of the SQSTM1/p62-based aggresome-like induced structures determines the sensitivity to parthanatos.

Overactivation of poly (ADP-ribose) polymerase-1 (PARP-1) triggers a noncanonical form of programmed cell death (PCD) called parthanatos, yet the mechanisms of its induction are not fully understood. We have recently demonstrated that the aggresome-like induced structures (ALIS) composed of the autophagy receptor SQSTM1/p62 and K48-linked polyubiquitinated proteins (p62-based ALIS) mediate parthanatos. In this study, we identified the D1 dopamine receptor agonist YM435 as a unique parthanatos inhibitor that acts as the disaggregating agent for the p62-based ALIS. We found that YM435 structurally reduces aggregability of the ALIS, and then increases its hydrophilicity and liquidity, which prevents parthanatos. Moreover, dopamine and L-DOPA, a dopamine precursor, also prevented parthanatos by reducing the aggregability of the ALIS. Together, these observations suggest that aggregability of the p62-based ALIS determines the sensitivity to parthanatos, and the pharmacological properties of YM435 that reduces the aggregability may be suitable for therapeutic drugs for parthanatos-related diseases such as neurodegenerative diseases.