Expression, purification and characterization of recombinant human serine proteinase inhibitor Kazal-type 6 (SPINK6) in Pichia pastoris

SPINK6 inhibits human airway serine proteases and restricts influenza virus activation

SPINK6 was identified in human skin as a cellular inhibitor of serine proteases of the KLK family. Airway serine proteases are required to cleave hemagglutinin (HA) of influenza A viruses (IAVs) to initiate an infection in the human airway. We hypothesized that SPINK6 may inhibit common airway serine proteases and restrict IAV activation. We demonstrate that SPINK6 specifically suppresses the proteolytic activity of HAT and KLK5, HAT- and KLK5-mediated HA cleavage, and restricts virus maturation and replication. SPINK6 constrains the activation of progeny virions and impairs viral growth; and vice versa, blocking endogenous SPINK6 enhances HA cleavage and viral growth in physiological-relevant human airway organoids where SPINK6 is intrinsically expressed. In IAV-infected mice, SPINK6 significantly suppresses viral growth and improves mouse survival. Notably, individuals carrying the higher SPINK6 expression allele were protected from human H7N9 infection. Collectively, SPINK6 is a novel host inhibitor of serine proteases in the human airway and restricts IAV activation.

Expression profiling revealed keratins and interleukins as potential biomarkers in squamous cell carcinoma of horn in Indian bullocks (Bos indicus)

Horn cancer is most prevalent in Bos indicus and poorly defined genetic landscape makes disease diagnosis and treatment difficult. In this study, RNA-Seq and data analysis using CLC Genomics Workbench was employed to identify biomarkers associated with horn cancer. As a result, a total of 149 genes were found significant differentially expressed in horn cancer samples compared to horn normal samples. The study revealed 'keratins' and 'interleukins' as apex groups of significant differentially expressed genes (DEGs). Functional analysis showed that the upregulated keratins support metastasis of tumor via cell proliferation, migration, and affecting cell stability, while downregulated interleukins along with other associated chemokine receptors deprive the immune response to tumor posing clear path for metastasis of horn cancer. Combi-action of both the group facilitates the tumor microenvironment to reproduce tumorigenesis. Analysis of pathways enriched in DEGs and exemplified protein-protein interaction network indicated actual role of DEGs in horn cancer at a fine level. Important effect of deregulated expression of keratin and interleukin genes in horn cancer enrolling their candidacy as potential biomarkers for horn cancer prognosis. This study appraises the possibility to mitigate horn cancer at fine resolution to extract attainable identification of prognostic molecular portraits.

Recombinant Inga Laurina Trypsin Inhibitor (ILTI) Production in Komagataella Phaffii Confirms Its Potential Anti-Biofilm Effect and Reveals an Anti-Tumoral Activity

Protease inhibitors have a broad biotechnological application ranging from medical drugs to anti-microbial agents. The Inga laurina trypsin inhibitor (ILTI) previously showed a great in vitro inhibitory effect under the adherence of Staphylococcus species, being a strong candidate for use as an anti-biofilm agent. Nevertheless, this is found in small quantities in its sources, which impairs its utilization at an industrial scale. Within this context, heterologous production using recombinant microorganisms is one of the best options to scale up the recombinant protein production. Thus, this work aimed at utilizing Komagataella phaffii to produce recombinant ILTI. For this, the vector pPIC9K+ILTI was constructed and inserted into the genome of the yeast K. phaffii, strain GS115. The protein expression was highest after 48 h using methanol 1%. A matrix-assisted laser desorption ionization⁻time-of-flight (MALDI⁻TOF) analysis was performed to confirm the production of the recombinant ILTI and its activity was investigated trough inhibitory assays using the synthetic substrate Nα-Benzoyl-D,L-arginine p-nitroanilide hydrochloride (BAPNA). Finally, recombinant ILTI (rILTI) was used in assays, showing that there was no significant difference between native and recombinant ILTI in its inhibitory activity in biofilm formation. Anti-tumor assay against Ehrlich ascites tumor (EAT) cells showed that rILTI has a potential anti-tumoral effect, showing the same effect as Melittin when incubated for 48 h in concentrations above 25 µg/mL. All together the results suggests broad applications for rILTI.

Serine protease inhibitor kazal-type 6 inhibits tumorigenesis of human hepatocellular carcinoma cells via its extracellular action

Hepatocellular carcinoma (HCC) causes significant medical burdens worldwide. Diagnosis, especially in the early stages, is still challenging. Therapeutic options are limited and often ineffective. Although several risk factors have been known important for development of HCC, the molecular basis of the process is rather complex and has not been fully understood. We have found that a subpopulation of HCC cells which are resistant to oncolytic parvovirus H1 superinfection highly express serine protease inhibitor Kazal-type 6 (SPINK6). This protein is specifically reduced in all HCC cell lines and tissues we analyzed. When upregulated, SPINK6 could suppress the malignant phenotypes of the HCC cells in several in vitro models. The putative tumor suppression role of SPINK6 is, however, independent of its protease inhibitory activity. To suppress the malignancy of HCC cells, SPINK6 has to be secreted to trigger signals which regulate an intracellular signaling molecule, ERK1/2, as well as a series of downstream factors involved in cell cycle progression, apoptosis and migration. Our study supports that SPINK6 is an important tumor suppressor in liver, and further investigations may help develop more effective diagnostic and therapeutic approaches.

Regulation of kallikrein-related peptidases in the skin – from physiology to diseases to therapeutic options

Kallikrein-related peptidases (KLKs) constitute a family of 15 highly conserved serine proteases, which show a tissue-specific expression profile. This made them valuable tumour expression markers. It became evident that KLKs are involved in many physiological processes like semen liquefaction and skin desquamation. More recently, we have learnt that they are involved in many pathophysiological conditions and diseases making them promising target of therapeutic intervention. Therefore, regulation of KLKs raised the interest of numerous reports. Herein, we summarise the current knowledge on KLKs regulation with an emphasis on skin-relevant KLKs regulation processes. Regulation of KLKs takes place on the level of transcription, on protease activation and on protease inactivation. A variety of protease inhibitors has been described to interact with KLKs including the irreversible serine protease inhibitors (SERPINs) and the reversible serine protease inhibitors of Kazal-type (SPINKs). In an attempt to integrate current knowledge, we propose that KLK regulation has credentials as targets for therapeutic intervention.

A potential Kazal-type serine protease inhibitor involves in kinetics of protease inhibition and bacteriostatic activity

Kazal-type serine protease inhibitor (KSPI) is a pancreatic secretary trypsin inhibitor which involves in various cellular component regulations including development and defense process. In this study, we have characterized a KSPI cDNA sequence of freshwater striped murrel fish Channa striatus (Cs) at molecular level. Cellular location analysis predicted that the CsKSPI was an extracellular protein. The domain analysis showed that the CsKSPI contains a Kazal domain at 47-103 along with its family signature between 61 and 83. Phylogenetically, CsKSPI is closely related to KSPI from Maylandia zebra and formed a sister group with mammals. The 2D structure of CsKSPI showed three α-helical regions which are connected with random coils, one helix at signal sequence and two at the Kazal domain region. The relative gene expression showed that the CsKSPI was highly expressed in gills and its expression was induced upon fungus (Aphanomyces invadans), bacteria (Aeromonas hydrophila) and poly I:C (a viral analogue) challenge. The CsKSPI recombinant protein was produced to characterize and study the CsKSPI gene specific functions. The recombinant CsKSPI strongly inhibited trypsin compared to other tested proteases. The results of the kinetic activity of CsKSPI against trypsin was V(max)s = 1.62 nmol/min, K(M)s = 0.21 mM and K(i)s = 15.37 nM. Moreover, the recombinant CsKSPI inhibited the growth of Gram-negative bacteria A. hydrophila at 20 μM and Gram-positive bacteria Bacillus subtilis at the MIC50 of 15 μM. Overall, the study indicated that the CsKSPI was a potential trypsin inhibitor which involves in antimicrobial activity.

Atomic resolution crystal structure of HV-BBI protease inhibitor from amphibian skin in complex with bovine trypsin

Protease inhibitors of the Bowman-Birk (BBI) family are commonly found in plants and animals where they play a protective role against invading pathogens. Here, we report an atomic resolution (1Å) crystal structure of a peptide inhibitor isolated from a skin secretion of a Chinese bamboo odorous frog Huia versabilis (HV-BBI) in complex with trypsin. HV-BBI shares significant similarities in sequence with a previously described inhibitor from a diskless-fingered odorous frog Odorrana graham (ORB). However, the latter is characterized by more than a 16,000 fold higher Ki against trypsin than HV-BBI. Comparative analysis of trypsin cocrystal structures of HV-BBI and ORB and additionally that of Sunflower Trypsin Inhibitor (SFTI-1) together with accessory information on the affinities of inhibitor variants allowed us to pinpoint the inhibitor moiety responsible for the observed large difference in activity and also to define the extent of modifications permissible within the common protease-binding loop scaffold of BBI inhibitors. We suggest that modifications outside of the inhibitory loop permit the evolution of specificity toward different enzymes characterized by trypsin-like specificity.

Antimicrobial activity of a honeybee (Apis cerana) venom Kazal-type serine protease inhibitor

Insect-derived Kazal-type serine protease inhibitors exhibit thrombin, elastase, plasmin, proteinase K, or subtilisin A inhibition activity, but so far, no functional roles for bee-derived Kazal-type serine protease inhibitors have been identified. In this study, a bee (Apis cerana) venom Kazal-type serine protease inhibitor (AcKTSPI) that acts as a microbial serine protease inhibitor was identified. AcKTSPI contained a single Kazal domain that displayed six conserved cysteine residues and a P1 threonine residue. AcKTSPI was expressed in the venom gland and was present as a 10-kDa peptide in bee venom. Recombinant AcKTSPI Kazal domain (AcKTSPI-Kd) expressed in baculovirus-infected insect cells demonstrated inhibitory activity against subtilisin A (Ki 67.03 nM) and proteinase K (Ki 91.53 nM), but not against α-chymotrypsin or trypsin, which implies a role for AcKTSPI as a microbial serine protease inhibitor. However, AcKTSPI-Kd exhibited no detectable inhibitory effects on factor Xa, thrombin, tissue plasminogen activator, or elastase. Additionally, AcKTSPI-Kd bound directly to Bacillus subtilis, Bacillus thuringiensis, Beauveria bassiana, and Fusarium graminearum but not to Escherichia coli. Consistent with these findings, AcKTSPI-Kd showed antibacterial activity against Gram-positive bacteria and antifungal activity against both plant-pathogenic and entomopathogenic fungi. These findings constitute molecular evidence that AcKTSPI acts as an inhibitor of microbial serine proteases. This paper provides a novel view of the antimicrobial functions of a bee venom Kazal-type serine protease inhibitor.

Cross-linking of SPINK6 by transglutaminases protects from epidermal proteases

Extracellular kallikrein-related peptidases (KLKs) are involved in the desquamation process and the initiation of epidermal inflammation by different mechanisms. Their action is tightly controlled by specific protease inhibitors. Recently, we have identified the serine protease inhibitor of Kazal-type (SPINK) 6 as a selective inhibitor of KLKs in human stratum corneum extracts. As SPINK6 is expressed in the same localization as transglutaminases (TGM) and contains TGM substrate motifs, SPINK6 was tested to be cross-linked in the epidermis. Recombinant SPINK6 was shown to be cross-linked to fibronectin (FN) by TGM1 by western blot analyses. Moreover, SPINK6 was cross-linked in epidermal extracts and cultured keratinocytes by immunoblotting analyses. The use of TGM1 and TGM3 resulted in different immunoreactivities in western blot analyses of SPINK6 and epidermal extracts, suggesting substrate specifities of different TGMs for SPINK6 cross-linking in the epidermis. Conjugated SPINK6 exhibited protease inhibitory activity in keratinocytes and stratum corneum extracts; cross-linked SPINK6 protected FN from KLK5-mediated cleavage, whereas a lower KLK-inhibiting SPINK6-GM mutation did not. In conclusion, we demonstrated that SPINK6 is cross-linked in keratinocytes and human epidermis and remains inhibitory active. Thus, cross-linked SPINK6 might protect specific substrates such as FN from KLK cleavage and contributes to the regulation of proteases in the epidermis.