The histidine phosphatase LHPP: an emerging player in cancer

Histidine Phosphorylation: Protein Kinases and Phosphatases

Phosphohistidine (pHis) is a reversible protein post-translational modification (PTM) that is currently poorly understood. The P-N bond in pHis is heat and acid-sensitive, making it more challenging to study than the canonical phosphoamino acids pSer, pThr, and pTyr. As advancements in the development of tools to study pHis have been made, the roles of pHis in cells are slowly being revealed. To date, a handful of enzymes responsible for controlling this modification have been identified, including the histidine kinases NME1 and NME2, as well as the phosphohistidine phosphatases PHPT1, LHPP, and PGAM5. These tools have also identified the substrates of these enzymes, granting new insights into previously unknown regulatory mechanisms. Here, we discuss the cellular function of pHis and how it is regulated on known pHis-containing proteins, as well as cellular mechanisms that regulate the activity of the pHis kinases and phosphatases themselves. We further discuss the role of the pHis kinases and phosphatases as potential tumor promoters or suppressors. Finally, we give an overview of various tools and methods currently used to study pHis biology. Given their breadth of functions, unraveling the role of pHis in mammalian systems promises radical new insights into existing and unexplored areas of cell biology.

[Progress in enrichment methods for protein N-phosphorylation]

Protein phosphorylation is one of the most common and important post-translational modifications that regulates almost all life processes. In particular, protein phosphorylation regulates the development of major diseases such as tumors, neurodegenerative diseases, and diabetes. For example, excessive phosphorylation of Tau protein can cause neurofibrillary tangles, leading to Alzheimer's disease. Therefore, large-scale methods for identifying protein phosphorylation must be developed. Rapid developmentin efficient enrichment methods and biological mass spectrometry technologies have enabled the large-scale identification of low-abundance protein O-phosphorylation modifications in, allowing for a more thorough study of their biological functions. The N-phosphorylation modifications that occur on the side-chain amino groups of histidine, arginine, and lysine have recently received increased attention. For example, the biological function of histidine phosphorylation in prokaryotes has been well studied; this type of modification regulates signal transduction and sugar metabolism. Two mammalian pHis kinases (NME1 and NME2) and three pHis phosphatases (PHPT1, LHPP, and PGAM5) have been successfully identified using various biological methods. N-Phosphorylation is involved in multiple biological processes, and its functions cannot be ignored. However, N-phosphorylation is unstable under acidic and thermal conditions owing to the poor chemical stability of the P-N bond. Unfortunately, the current O-phosphorylation enrichment method, which relies on acidic conditions, is unsuitable for N-phosphorylation enrichment, resulting in a serious lag in the large-scale identification of protein N-phosphorylation. The lack of enrichment methods has also seriously hindered studies on the biological functions of N-phosphorylation. Therefore, the development of efficient enrichment methods that target protein N-phosphorylation is an urgent undertaking. Research on N-phosphorylation proteome enrichment methods is limited, hindering functional research. Thus, summarizing such methods is necessary to promote further functional research. This article introduces the structural characteristics and reported biological functions of protein N-phosphorylation, reviews the protein N-phosphorylation modification enrichment methods developed over the past two decades, and analyzes the advantages and disadvantages of each method. In this study, both antibody-based and nonantibody-dependent methods are described in detail. Owing to the stability of the molecular structure of histidine, the antibody method is currently limited to histidine phosphorylation enrichment research. Future studies will focus on the development of new enrichment ligands. Moreover, research on ligands will promote studies on other nonconventional phosphorylation targets, such as two acyl-phosphates (pAsp, pGlu) and S-phosphate (pCys). In summary, this review provides a detailed analysis of the history and development directions of N-phosphorylation enrichment methods.

Oncolytic adenovirus encoding LHPP exerts potent antitumor effect in lung cancer

LHPP has been shown to be a new tumor suppressor, and has a tendency to be under-expressed in a variety of cancers. Oncolytic virotheray is a promising therapeutics for lung cancer in recent decade years. Here we successfully constructed a new recombinant oncolytic adenovirus GD55-LHPP and investigated the effect of GD55-LHPP on the growth of lung cancer cells in vitro and in vivo. The results showed that LHPP had lower expression in either lung cancer cells or clinical lung cancer tissues compared with normal cells or tissues, and GD55-LHPP effectively mediated LHPP expression in lung cancer cells. GD55-LHPP could effectively inhibit the proliferation of lung cancer cell lines and rarely affected normal cell growth. Mechanically, the oncolytic adenovirus GD55-LHPP was able to induce stronger apoptosis of lung cancer cells compared with GD55 through the activation of caspase signal pathway. Notably, GD55-LHPP also activated autophagy-related signal pathway. Further, GD55-LHPP efficiently inhibited tumor growth in lung cancer xenograft in mice and prolonged animal survival rate compared with the control GD55 or PBS. In conclusion, the novel construct GD55-LHPP provides a valuable strategy for lung cancer-targeted therapy and develop the role of tumor suppress gene LHPP in lung cancer gene therapy.

LHPP expression in triple-negative breast cancer promotes tumor growth and metastasis by modulating the tumor microenvironment

Triple-negative breast cancer (TNBC) is a highly aggressive and metastatic form of breast cancer that lacks an effective targeted therapy. To identify new therapeutic targets, we investigated the phosphohistidine phosphatase, LHPP, which has been implicated in the development of several types of cancer. However, the full significance of LHPP in cancer progression remains unclear due to our limited understanding of its molecular mechanism. We found that levels of the LHPP phosphohistidine phosphatase were significantly increased in human breast cancer patients compared to normal adjacent tissues, with the highest levels in the TNBC subtype. When LHPP was knocked out in the MDA-MB-231 human TNBC cell line, cell proliferation, wound healing capacity, and invasion were significantly reduced. However, LHPP knockout in TNBC cells did not affect the phosphohistidine protein levels. Interestingly, LHPP knockout in MDA-MB-231 cells delayed tumor growth and reduced metastasis when orthotopically transplanted into mouse mammary glands. To investigate LHPP's role in breast cancer progression, we used next-generation sequencing and proximity-labeling proteomics, and found that LHPP regulates gene expression in chemokine-mediated signaling and actin cytoskeleton organization. Depletion of LHPP reduced the presence of tumor-infiltrating macrophages in mouse xenografts. Our results uncover a new tumor promoter role for LHPP phosphohistidine phosphatase in TNBC and suggest that targeting LHPP phosphatase could be a potential therapeutic strategy for TNBC.

Phospholysine phosphohistidine inorganic pyrophosphate phosphatase suppresses insulin-like growth factor 1 receptor expression to inhibit cell adhesion and proliferation in gastric cancer

Phospholysine phosphohistidine inorganic pyrophosphate phosphatase (LHPP) has recently emerged as a novel tumor suppressor. Researchers have observed that LHPP plays a crucial role in inhibiting proliferation, growth, migration, invasion, and cell metabolism across various cancers. Nevertheless, the specific functions and underlying mechanisms of LHPP as a tumor suppressor in gastric cancer (GC) require further exploration. The expression of LHPP was assessed in human GC specimens and cell lines. Various assays were employed to evaluate the impact of LHPP on GC cells. RNA sequencing and Gene Set Enrichment Analysis were conducted to unravel the mechanism through which LHPP regulates GC cell behavior. Additionally, xenograft nude mouse models were utilized to investigate the in vivo effects of LHPP. The findings indicate that LHPP, functioning as a tumor suppressor, is downregulated in both GC tissues and cells. LHPP emerges as an independent risk factor for GC patients, and its expression level exhibits a positive correlation with patient prognosis. LHPP exerts inhibitory effects on the adhesion and proliferation of GC cells by suppressing the expression of insulin-like growth factor 1 receptor (IGF1R) and modulating downstream signaling pathways. Consequently, LHPP holds potential as a biomarker for targeted therapy involving IGF1R inhibition in GC patients.

The histidine phosphatase LHPP of Penaeus vannamei is involved in shrimp hemocytes apoptosis

LHPP (Phospholysine Phosphohistidine Inorganic Pyrophosphate Phosphatase) is a protein histidine phosphatase that modulates a hidden posttranslational modification called histidine phosphorylation. LHPP also acts as a tumor suppressor, which plays a pivotal role in various cellular processes. However, whether LHPP participates in the regulation of invertebrate's immunity is still unknown. Here we characterized a LHPP homolog in P. vannamei (designated PvLHPP), with a 807 bp length of open reading frame (ORF) encoding a putative protein of 268 amino acids. Sequence analysis revealed that PvLHPP contains a typical hydrolase 6 and hydrolase-like domain, which was conserved from invertebrate to vertebrate. PvLHPP was ubiquitously expressed in tissues and induced in hemocyte and hepatopancreas by Vibrio parahaemolyticus, Streptococcus iniae and white spot syndrome virus (WSSV) challenge, indicating that PvLHPP participated in the immune responses. Moreover, silencing of PvLHPP followed by V. parahaemolyticus inhibited hemocyte apoptosis. This study enriches our current insight on shrimp immunity, and provides novel perspective to understand immune-regulatory role of PvLHPP.

LHPP Inhibits the Viability, Migration, and Proliferation of PDAC Cells and Significantly Affects the Expression of SDC1 and S100p

INTRODUCTION

Pancreatic ductal adenocarcinoma (PDAC) is a highly aggressive malignancy with a poor response to chemotherapy and an extremely poor prognosis. Recent studies have revealed that phospholysine phosphohistidine inorganic pyrophosphate phosphatase (LHPP) can inhibit the growth of various cancers. Therefore, the current study was conducted to investigate the antitumor effects of LHPP in PDAC and to explore its mechanism using proteomics analysis.

METHODS AND RESULTS

Immunohistochemical analysis of clinical samples demonstrated that LHPP expression levels were lower in tumor tissues compared to adjacent nontumor tissues. Moreover, multivariate COX regression analysis showed that LHPP expression level was an independent prognostic factor for the patients with PDAC. Patients with high LHPP expression had a better prognosis. The lentiviral vectors for normal control (NC), LHPP knockdown (KD), and LHPP overexpression (OE) were infected with BxPC-3 and PANC-1 cell lines. Cell counting kit-8 assay, Transwell assay, and flow cytometry analyses showed that LHPP overexpression significantly inhibited the cell viability, migration, and proliferation of BxPC-3 and PANC-1 cells. Moreover, xenograft tumor model demonstrated that LHPP overexpression inhibited xenograft tumor growth in vivo. Subsequently, proteins with significantly altered expression in BxPC-3 cells after lentivirus infection were detected using proteomics analyses. Interestingly, compared to the NC group, the expression of Syndecan 1 (SDC1) was significantly upregulated in the KD group, while that of S100P was significantly downregulated in the OE group.

CONCLUSION

LHPP might emerge as an important target for delaying the advancement of PDAC, thereby providing a novel therapeutic approach for the treatment of PDAC.