Dipeptidyl peptidase IV is involved in the cellulose-responsive induction of cellulose biomass-degrading enzyme genes in Aspergillus aculeatus

C-terminus of serine-arginine protein kinase-like protein, SrpkF, is involved in conidiophore formation and hyphal growth under salt stress in Aspergillus aculeatus

The serine-arginine protein kinase-like protein, SrpkF, was identified as a regulator for the cellulose-responsive induction of cellulase genes in Aspergillus aculeatus. To analyze various aspects of SrpkF function, we examined the growth of the control strain (MR12); C-terminus deletion mutant, which produced SrpkF1-327 (ΔCsrpkF); whole gene-deletion mutant of srpkF (ΔsrpkF), srpkF overexpressing strain (OEsprkF); and the complemented strain (srpkF+) under various stress conditions. All test strains grew normally on minimal medium under control, high salt (1.5 M KCl), and high osmolality (2.0 M sorbitol and 1.0 M sucrose). However, only ΔCsrpkF showed reduced conidiation on 1.0 M NaCl media. Conidiation of ΔCsrpkF on 1.0 M NaCl media was reduced to 12% compared with that of srpkF+. Further, when OEsprkF and ΔCsrpkF were pre-cultured under salt stress conditions, germination under salt stress conditions was enhanced in both strains. By contrast, deletion of srpkF did not affect hyphal growth and conidiation under the same conditions. We then quantified the transcripts of the regulators involved in the central asexual conidiation pathway in A. aculeatus. The findings revealed that the expression of brlA, abaA, wetA, and vosA was reduced in ΔCsrpkF under salt stress. These data suggest that in A. aculeatus, SrpkF regulates conidiophore development. The C-terminus of SrpkF seems to be important for regulating SrpkF function in response to culture conditions such as salt stress.

Independent, cooperative regulation of cellulolytic genes by paralogous transcription factors ClbR and ClbR2 in Aspergillus aculeatus

The cellobiose-responsive regulator ClbR, a Zn(II)2Cys6 binuclear-cluster transcription factor, is a positive regulator of carbohydrate-active enzyme (CAZyme) genes responsive to cellulose in Aspergillus aculeatus. Because Zn(II)2Cys6 transcription factors tend to dimerize with proteins of the same family, we searched for a counterpart of ClbR and identified ClbR2, which is 42% identical to ClbR, as an interacting partner of ClbR by yeast two-hybrid screening. Genetic analyses suggested that ClbR and ClbR2 cooperatively regulate the expression of CAZyme genes in response to cellulose and 1,4-β-mannobiose in A. aculeatus. CAZyme genes under the control of the transcription factor ManR were regulated by ClbR and ClbR2, whereas those controlled by the transcription factor XlnR were regulated by ClbR, but not ClbR2. These findings suggest that ClbR participates in multiple regulatory pathways in A. aculeatus by altering an interacting factor.

A new function of a putative UDP-glucose 4-epimerase on the expression of glycoside hydrolase genes in Aspergillus aculeatus

In order to figure out the induction mechanisms of glycoside hydrolase genes in Aspergillus aculeatus, we screened approximately 9,000 transfer DNA (T-DNA)-inserted mutants for positive regulators involved in the induction. Since the mutants possess the orotidine 5'-monophosphate decarboxylase gene as a reporter gene to monitor the cellulose-responsive expression of the cellobiohydrolase I gene (cbhI), candidate strains were isolated by counterselection against 5-fluoroorotic acid (5-FOA). One 5-FOA-resistant mutant harboring the T-DNA at the uge5 locus showed reduced cellulose utilization and cbhI expression. A. aculeatus Uge5 is homologous to Aspergillus fumigatus uge5 (Afu5g10780; E-value, 0.0; identities, 93%), which catalyzes the conversion of uridine diphosphate (UDP)-glucose to UDP-galactopyranose. The uge5 deletion mutant in A. aculeatus (Δuge5) showed reduced conidium formation on minimal media supplemented with galactose, locust bean gum (LBG), and guar gum as a carbon source. β-1,4-Endoglucanase and β-1,4-mannanase production in submerged culture containing LBG was reduced to 10% and 6% of the control strain at day 5, respectively, but no difference was observed in cultures containing wheat bran. The expression of major cellulolytic and mannolytic genes in the presence of mannobiose in Δuge5 was reduced to less than 15% of the control strain, while cellobiose-responsive expression was only modestly reduced at early inducing time points. Since all test genes were controlled by a transcription factor ManR, these data demonstrate that Uge5 is involved in inducer-dependent selective expression of genes controlled via ManR. KEY POINTS: • UDP-glucose 4-epimerase (Uge5) regulates expression of glycosyl hydrolase genes. • ManR regulates both cellobiose- and mannobiose-responsive expression. • Uge5 plays a key role in mannobiose-responsive expression.

Serine-arginine protein kinase-like protein, SrpkF, stimulates both cellobiose-responsive and D-xylose-responsive signaling pathways in Aspergillus aculeatus

Aspergillus aculeatus produces cellulolytic enzymes in the presence of their substrates. We screened a library of 12,000 A. aculeatus T-DNA-inserted mutants to identify a regulatory factor involved in the expression of their enzyme genes in response to inducers. We found one mutant that reduced the expression of FIII-avicelase (chbI) in response to cellulose. T-DNA was inserted into a putative protein kinase gene similar to AN10082 in A. nidulans, serine-arginine protein kinase F, SrpkF. Fold increases in srpkF gene expression in response to various carbon sources were 2.3 (D-xylose), 44 (Avicel^®), 59 (Bacto^™ Tryptone), and 98 (no carbon) compared with D-glucose. Deletion of srpkF in A. aculeatus resulted in a significant reduction in cellulose-responsive expression of chbI, hydrocellulase (cel7b), and FIb-xylanase (xynIb) genes at an early induction phase. Further, the srpkF-overexpressing strain showed upregulation of the srpkF gene from four- to nine-fold higher than in the control strain. srpkF overexpression upregulated cbhI and cel7b in response to cellobiose and the FI-carboxymethyl cellulase gene (cmc1) and xynIb in response to D-xylose. However, the srpkF deletion did not affect the expression of xynIb in response to D-xylose due to the less expression of srpkF under the D-xylose condition. Our data demonstrate that SrpkF is primarily involved in cellulose-responsive expression, though it has a potential to stimulate gene expression in response to both cellobiose and D-xylose in A. aculeatus.

A component of the septation initiation network complex, AaSepM, is involved in multiple cellulose-responsive signaling pathways in Aspergillus aculeatus

Various carbohydrate-active enzymes in Aspergillus are produced in response to physiological inducers, which is regulated at the transcriptional level. To elucidate the induction mechanisms in Aspergillus, we screened for new regulators involved in cellulose-responsive induction from approximately 10,000 Aspergillus aculeatus T-DNA-inserted mutants. We constructed the T-DNA-inserted mutant library using the host strain harboring the orotidine 5'-monophosphate decarboxylase gene (pyrG) under the control of the FIII-avicelase gene (cbhI) promoter. Thus, candidate mutants deficient in cellulose-responsive induction were positively screened via counter selection against 5-fluoroorotic acid (5-FOA). Among less than two hundred 5-FOA-resistant mutants, one mutant that the T-DNA inserted into the AasepM locus reduced the cbhI expression in response to cellulose. Since AaSepM is similar to Schizosaccharomyces pombe Cdc14p (E-value, 2e-20; identities, 33%), which is a component of the septation initiation network (SIN)-complex, we constructed an AasepM deletion mutant (ΔAasepM). We analyzed the expression of cellulase and xylanase genes in response to cellulose, septation, and conidiation in ΔAasepM. The AasepM deletion leads to delayed septation and decreased formation of the conidium chain in A. aculeatus but does not affect hyphal growth on minimal media. We also confirmed AaSepM's involvement in multiple cellulose-responsive signaling pathways of cellulase and xylanase genes under the control of the ManR-dependent, XlnR-dependent, and ManR- and XlnR-independent signaling pathways. KEY POINTS : • A new regulator for cellulolytic gene expression has been identified. • AaSepM is involved in septation and conidiation in A. aculeatus. • AasepM is involved in multiple cellulose-responsive signaling pathways.

Chemical genetic approach using β-rubromycin reveals that a RIO kinase-like protein is involved in morphological development in Phytophthora infestans

To characterize the molecular mechanisms underlying life-stage transitions in Phytophthora infestans, we initiated a chemical genetics approach by screening for a stage-specific inhibitor of morphological development from microbial culture extracts prepared mostly from actinomycetes from soil in Japan. Of the more than 700 extracts, one consistently inhibited Ph. infestans cyst germination. Purification and identification of the active compound by ESI–MS, ¹H-NMR, and ¹³C-NMR identified β-rubromycin as the inhibitor of cyst germination (IC₅₀ = 19.8 μg/L); β-rubromycin did not inhibit growth on rye media, sporangium formation, zoospore release, cyst formation, or appressorium formation in Ph. infestans. Further analyses revealed that β-rubromycin inhibited the germination of cysts and oospores in Pythium aphanidermatum. A chemical genetic approach revealed that β-rubromycin stimulated the expression of RIO kinase-like gene (PITG_04584) by 60-fold in Ph. infestans. Genetic analyses revealed that PITG_04584, which lacks close non-oomycete relatives, was involved in zoosporogenesis, cyst germination, and appressorium formation in Ph. infestans. These data imply that further functional analyses of PITG_04584 may contribute to new methods to suppress diseases caused by oomycetes.

Meta-analysis on the efficacy and safety of SGLT2 inhibitors and incretin based agents combination therapy vs. SGLT2i alone or add-on to metformin in type 2 diabetes

We aimed to determine whether sodium-glucose cotransporter type 2 inhibitors (SGLT2is) and incretin-based agents combination therapy produces more benefits than SGLT2is alone in patients with type 2 diabetes mellitus (T2DM). PubMed, Embase, and the Cochrane Library were searched for randomized controlled trials (RCTs) comparing SGLT2is plus Dipeptidyl-Peptidase 4 inhibitors (SGLT2is/DPP4is) or glucagon like peptide-1 receptor agonists (SGLT2is/GLP-1RAs) against SGLT2is as monotherapy or add-on to metformin in T2DMs. A total of 13 studies with 7350 participants were included. Combination with GLP-1RAs exhibited more HbA1c reduction (WMD: -0.8; 95% CI, -1.14 to -0.45%), weight loss (-1.46; 95% CI, -2.38 to -0.54 kg), and systolic blood pressure (SBP) reduction (-2.88; 95% CI, -4.52 to -1.25 mmHg) versus SGLT2is alone but increased the gastrointestinal disorder risk (RR: 1.68; 95% CI, 1.14-2.47). Combination with DPP4is exhibited an extra effect on HbA1c reduction (-0.47; 95% CI, -0.58 to -0.37%), a neutral effect on weight (0.19; 95% CI, -0.11 to 0.48 kg) and SBP (-0.01; 95% CI, -0.85 to 0.63 mmHg), and ameliorated the genital infections risk (0.73; 95% CI, 0.54-0.97) versus SGLT2is. Meta-regression indicated the hypoglycemic efficacy of SGLT2is/DPP4is is higher in Asians than in other ethnics, and the differences in BMI across ethnic groups may mediate this effect. SGLT2is and incretin-based agents combination therapy is efficacious and safe versus SGLT2is alone in T2DMs. Particularly, combination with GLP-1RAs shows additional benefits to glycemic, weight, and SBP control to a larger extent than DPP4is, while combination with DPP4is ameliorates the risk for genital infection seen with SGLT2is. We highlight the need for individualized treatment related to the selection of this novel combination therapy.

Dipeptidyl peptidase-4 inhibitors moderate the risk of genitourinary tract infections associated with sodium-glucose co-transporter-2 inhibitors

Genitourinary tract infections (GUTIs) are the most common adverse event (AE) occurring during therapy with sodium-glucose co-transporter-2 (SGLT2) inhibitors. We evaluated whether dipeptidyl peptidase-4 inhibitors moderate the risk of GUTI during SGLT2 inhibitor therapy, using two approaches. First, we screened the literature for randomized controlled trials (RCTs) directly comparing the frequency of GUTIs in patients receiving DPP-4 inhibitor/SGLT2 inhibitor combination therapy vs those receiving an SGLT2 inhibitor only. In the five trials we retrieved, the pooled risk ratio for genital tract infections (GTIs) in patients on DPP-4 inhibitor/SGLT2 inhibitor combination therapy vs those on SGLT2 inhibitors alone was 0.51 (95% confidence interval [CI] 0.28-0.92). Second, we found that within the Food and Drug Administration AE Reporting System, the frequency of GUTIs among reports listing both SGLT2 and DPP-4 inhibitors as suspect or concomitant drugs was significantly lower than among reports listing SGLT2 inhibitors without DPP-4 inhibitors, with a proportional reporting ratio of 0.74 (95% CI 0.61-0.90). In conclusion, in RCTs and in a large pharmacovigilance database, combination therapy with a DPP-4 inhibitor appears to reduce the frequency of G(U)TIs associated with SGLT2 inhibitors.