Modulators of MAPK pathway activity during filamentous growth in Saccharomyces cerevisiae

Mitogen-activated protein kinase (MAPK) pathways control the response to intrinsic and extrinsic stimuli. In the budding yeast Saccharomyces cerevisiae, cells undergo filamentous growth, which is regulated by the fMAPK pathway. To better understand the regulation of the fMAPK pathway, a genetic screen was performed to identify spontaneous mutants with elevated activity of an fMAPK-pathway dependent growth reporter (ste4 FUS1-HIS3). In total, 159 mutants were isolated and analyzed by secondary screens for invasive growth by the plate-washing assay, and filament formation by microscopy. Thirty-two mutants were selected for whole-genome sequencing, which identified new alleles in genes encoding known regulators of the fMAPK pathway. These included gain-of-function alleles in STE11, which encodes the MAPKKK, as well as loss-of-function alleles in KSS1, which encodes the MAP kinase, and loss-of-function alleles in RGA1, which encodes a GTPase activating protein (GAP) for CDC42. New alleles in previously identified pathway modulators were also uncovered in ALY1, AIM44, RCK2, IRA2, REG1 and in genes that regulate protein folding (KAR2), glycosylation (MNN4), and turnover (BLM10). C-terminal truncations in the transcription factor Ste12p were also uncovered that resulted in elevated reporter activity, identifying an inhibitory domain of the protein from residues 491 to 688. We also find that a diversity of filamentous growth phenotypes can result from combinatorial effects of multiple mutations and by loss of different regulators of the response. The alleles identified here expand the connections surrounding MAPK pathway regulation and reveal new features of proteins that function in the signaling cascade.

Modulators of MAPK pathway activity during filamentous growth in Saccharomyces cerevisiae

Mitogen-activated protein kinase (MAPK) pathways control the response to intrinsic and extrinsic stimuli. In the budding yeast Saccharomyces cerevisiae, cells undergo filamentous growth, which is regulated by the fMAPK pathway. To better understand the regulation of the fMAPK pathway, a genetic screen was performed to identify spontaneous mutants with elevated activity of an fMAPK-pathway dependent growth reporter (ste4 FUS1-HIS3). In total, 159 mutants were isolated and analyzed by secondary screens for invasive growth by the plate-washing assay, and filament formation by microscopy. Thirty-two mutants were selected for whole-genome sequencing, which identified new alleles in genes encoding known regulators of the fMAPK pathway. These included gain-of-function alleles in STE11, which encodes the MAPKKK, as well as loss-of-function alleles in KSS1, which encodes the MAP kinase, and RGA1, which encodes a GTPase activating protein (GAP) for CDC42. New alleles in previously identified pathway modulators were also uncovered in ALY1, AIM44, RCK2, IRA2, REG1 and in genes that regulate protein folding (KAR2), glycosylation (MNN4), and turnover (BLM10). C-terminal truncations in the transcription factor Ste12p were also uncovered that resulted in elevated reporter activity, presumably identifying an inhibitory domain in the C-terminus of the protein. We also show that a wide variety of filamentous growth phenotypes result from mutations in different regulators of the response. The alleles identified here expand the connections surrounding MAPK pathway regulation and reveal new features of proteins that function in the signaling cascade.

The Negative Regulative Roles of BdPGRPs in the Imd Signaling Pathway of Bactrocera dorsalis

Peptidoglycan recognition proteins (PGRPs) are key regulators in insects' immune response, functioning as sensors to detect invading pathogens and as scavengers of peptidoglycan (PGN) to reduce immune overreaction. However, the exact function of PGRPs in Bactrocera dorsalis is still unclear. In this study, we identified and functionally characterized the genes BdPGRP-LB, BdPGRP-SB₁ and BdPGRP-SC₂ in B. dorsalis. The results showed that BdPGRP-LB, BdPGRP-SB₁ and BdPGRP-SC₂ all have an amidase-2 domain, which has been shown to have N-Acetylmuramoyl-l-Alanine amidase activity. The transcriptional levels of BdPGRP-LB and BdPGRP-SC₂ were both high in adult stages and midgut tissues; BdPGRP-SB₁ was found most abundantly expressed in the 2nd instar larvae stage and adult fat body. The expression of BdPGRP-LB and BdPGRP-SB₁ and AMPs were significantly up-regulated after injury infected with Escherichia coli at different time points; however, the expression of BdPGRP-SC₂ was reduced at 9 h, 24 h and 48 h following inoculation with E. coli. By injection of dsRNA, BdPGRP-LB, BdPGRP-SB₁ and BdPGRP-SC₂ were knocked down by RNA-interference. Silencing of BdPGRP-LB, BdPGRP-SB₁ and BdPGRP-SC₂ separately in flies resulted in over-activation of the Imd signaling pathway after bacterial challenge. The survival rate of the ds-PGRPs group was significantly reduced compared with the ds-egfp group after bacterial infection. Taken together, our results demonstrated that three catalytic PGRPs family genes, BdPGRP-LB, BdPGRP-SB₁ and BdPGRP-SC₂, are important negative regulators of the Imd pathway in B. dorsalis.

Suppression of Interferon-α Treatment Response by Host Negative Factors in Hepatitis B Virus Infection

Chronic hepatitis B virus (CHB) infection remains a major global public health issue for which there is still lacking effective curative treatment. Interferon-α (IFN-α) and its pegylated form have been approved as an anti-HBV drug with the advantage of antiviral activity and host immunity against HBV infection enhancement, however, IFN-α treatment failure in CHB patients is a challenging obstacle with 70% of CHB patients respond poorly to exogenous IFN-α treatment. The IFN-α treatment response is negatively regulated by both viral and host factors, and the role of viral factors has been extensively illustrated, while much less attention has been paid to host negative factors. Here, we summarized evidence of host negative regulators and parameters involved in IFN-α therapy failure, review the mechanisms responsible for these effects, and discuss the possible improvement of IFN-based therapy and the rationale of combining the inhibitors of negative regulators in achieving an HBV cure.

Thymoquinone Suppresses Cell Proliferation and Enhances Apoptosis of HL60 Leukemia Cells through Re-Expression of JAK/STAT Negative Regulators

Objective:

The natural compound, thymoquinone (TQ) has demonstrated potential anticancer properties in inhibiting cell proliferation and promoting apoptosis in myeloid leukemia cells, breast cancer cells, and others. However, the effect mechanism of TQ on AML cells still not fully understood. In this study, the authors examined the effects of TQ on the expression of JAK/STAT-negative regulator genes SOCS-1, SOCS-3, and SHP-1, and their consequences on cell proliferation and apoptosis in HL60 leukemia cells.

Methods:

MTT and trypan blue exclusion tests were conducted to determine the 50% inhibitory concentration (IC50) and cell proliferation. FITC Annexin and Guava^® reagent were used to study the cell apoptosis and examine the cell cycle phases, respectively. The expression of JAK/STAT-negative regulator genes, SOCS-1, SOCS-3, and SHP-1, was investigated using reverse transcriptase- quantitative PCR (RT-qPCR).

Results:

TQ demonstrated a potential inhibition of HL60 cell proliferation and a significant increase in apoptotic cells in dose and time-dependent manner. TQ significantly induced cycle arrest at G0-G1 phase (P < 0.001) and enhanced the re-expression of JAK/STAT-negative regulator genes.

Conclusion:

TQ potentially inhibited HL60 cell proliferation and significantly increased apoptosis with re-expression of JAK/STAT-negative regulator genes suggesting that TQ could be a new therapeutic candidate for leukemia therapy.

Negative regulators of STAT3 signaling pathway in cancers

STAT3 is the most ubiquitous member of the STAT family and involved in many biological processes, such as cell proliferation, differentiation, and apoptosis. Mounting evidence has revealed that STAT3 is aberrantly activated in many malignant tumors and plays a critical role in cancer progression. STAT3 is usually regarded as an effective molecular target for cancer treatment, and abolishing the STAT3 activity may diminish tumor growth and metastasis. Recent studies have shown that negative regulators of STAT3 signaling such as PIAS, SOCS, and PTP, can effectively retard tumor progression. However, PIAS, SOCS, and PTP have also been reported to correlate with tumor malignancy, and their biological function in tumorigenesis and antitumor therapy are somewhat controversial. In this review, we summarize actual knowledge on the negative regulators of STAT3 in tumors, and focus on the potential role of PIAS, SOCS, and PTP in cancer treatment. Furthermore, we also outline the STAT3 inhibitors that have entered clinical trials. Targeting STAT3 seems to be a promising strategy in cancer therapy.

Cellular and molecular mechanisms involved in the resolution of innate leukocyte inflammation

Inflammation is a host response to infection or damage and is vital for clearing pathogens and host debris. When this resolution fails to occur, chronic inflammation ensues. Chronic inflammation is typically characterized as a low-grade, persistent inflammatory process that can last for months or even years. This differs from acute inflammation, which is typically a fast, robust response to a stimulus followed by resolution with return to homeostasis. Inflammation resolution occurs through a variety of cellular processes and signaling components that act as "brakes" to keep inflammation in check. In cases of chronic inflammation, these "brakes" are often dysfunctional. Due to its prevalent association with chronic diseases, there is growing interest in characterizing these negative regulators and their cellular effects in innate leukocytes. In this review, we aim to describe key cellular and molecular homeostatic regulators of innate leukocytes, with particular attention to the emerging regulatory processes of autophagy and lysosomal fusion during inflammation resolution.

Negative regulators of platelet activation and adhesion

Platelets are small anucleated cells that constantly patrol the cardiovascular system to preserve its integrity and prevent excessive blood loss where the vessel lining is breached. Their key challenge is to form a hemostatic plug under conditions of high shear forces. To do so, platelets have evolved a molecular machinery that enables them to sense trace amounts of signals at the site of damage and to rapidly shift from a non-adhesive to a pro-adhesive state. However, this highly efficient molecular machinery can also lead to unintended platelet activation and cause clinical complications such as thrombocytopenia and thrombosis. Thus, several checkpoints are in place to tightly control platelet activation and adhesiveness in space and time. In this review, we will discuss select negative regulators of platelet activation, which are critical to maintain patrolling platelets in a quiescent, non-adhesive state and/or to limit platelet adhesion to sites of injury.

Melioidosis and glanders modulation of the innate immune system: barriers to current and future vaccine approaches

Burkholderia pseudomallei and Burkholderia mallei are pathogenic bacteria causing fatal infections in animals and humans. Both organisms are classified as Tier 1 Select Agents owing to their highly fatal nature, potential/prior use as bioweapons, severity of disease via respiratory exposure, intrinsic resistance to antibiotics, and lack of a current vaccine. Disease manifestations range from acute septicemia to chronic infection, wherein the facultative intracellular lifestyle of these organisms promotes persistence within a broad range of hosts. This ability to thrive intracellularly is thought to be related to exploitation of host immune response signaling pathways. There are currently considerable gaps in our understanding of the molecular strategies employed by these pathogens to modulate these pathways and evade intracellular killing. A better understanding of the specific molecular basis for dysregulation of host immune responses by these organisms will provide a stronger platform to identify novel vaccine targets and develop effective countermeasures.