A bacterial tyrosine phosphatase modulates cell proliferation through targeting RGCC

Abstract

Tyrosine phosphatases are often weaponized by bacteria colonizing mucosal barriers to manipulate host cell signal transduction pathways. Porphyromonas gingivalis is a periodontal pathogen and emerging oncopathogen which interferes with gingival epithelial cell proliferation and migration, and induces a partial epithelial mesenchymal transition. P. gingivalis produces two tyrosine phosphatases, and we show here that the low molecular weight tyrosine phosphatase, Ltp1, is secreted within gingival epithelial cells and translocates to the nucleus. An ltp1 mutant of P. gingivalis showed a diminished ability to induce epithelial cell migration and proliferation. Ltp1 was also required for the transcriptional upregulation of Regulator of Growth and Cell Cycle (RGCC), one of the most differentially expressed genes in epithelial cells resulting from P. gingivalis infection. A phosphoarray and siRNA showed that P. gingivalis controlled RGCC expression through Akt, which was activated by phosphorylation on S473. Akt activation is opposed by PTEN, and P. gingivalis decreased the amount of PTEN in epithelial cells. Ectopically expressed Ltp1 bound to PTEN, and reduced phosphorylation of PTEN at Y336 which controls proteasomal degradation. Ltp-1 induced loss of PTEN stability was prevented by chemical inhibition of the proteosome. Knockdown of RGCC suppressed upregulation of Zeb2 and mesenchymal markers by P. gingivalis. RGCC inhibition was also accompanied by a reduction in production of the proinflammatory cytokine IL-6 in response to P. gingivalis. Elevated IL-6 levels can contribute to periodontal destruction, and the ltp1 mutant of P. gingivalis incited less bone loss compared to the parental strain in a murine model of periodontal disease. These results show that P. gingivalis can deliver Ltp1 within gingival epithelial cells, and establish PTEN as the target for Ltp1 phosphatase activity. Disruption of the Akt1/RGCC signaling axis by Ltp1 facilitates P. gingivalis-induced increases in epithelial cell migration, proliferation, EMT and inflammatory cytokine production.

Protein Tyrosine and Serine/Threonine Phosphorylation in Oral Bacterial Dysbiosis and Bacteria-Host Interaction

“…In summary, SerB can promote bacterial invasion of the host, allowing it to continue to exert its full pathogenic potential. Interestingly, it has very recently been reported that the tyrosine phosphatase (Ltp1) can also be secreted by P. gingivalis and appears in both the cytoplasm and nucleus of gingival epithelial cells ( Liu et al., 2021 ). The secreted Ltp1 can bind to phosphatase and tensin homolog (PTEN) and dephosphorylate its Y336 residue, resulting in the degradation of PTEN.…”

“…PTEN is a classic negative regulator of phosphoinositide 3-kinases/protein kinase B (PI3K/Akt). Thus, the inhibition of PTEN by Ltp1 could further activate PI3K/Akt and its downstream regulator of the cell cycle (RGCC), promoting the migration, proliferation and epithelial mesenchymal transition of epithelial cells ( Liu et al., 2021 ) ( Figure 5 ).…”

Tyrosine Kinases and Phosphatases: Enablers of the Porphyromonas gingivalis Lifestyle

“…Bacterial LMW-LTPs can also be secreted by yet to be defined mechanisms [ 42 , 43 ], and in the case of PtpA of Mycobacterium tuberculosis , enter into host cell nuclei [ 43 ]. P. gingivalis can also introduce Ltp1 directly into gingival epithelial cells where it can translocate to the nucleus [ 44 ]. As Ltp1 lacks the consensus sequence for recognition by the Type IX secretion system, the secretion process remains to be established.…”

“…An intracellular location will protect the enzyme from inactivation by metabolites such as pABA and peroxide produced by other organisms in the extracellular environment. Intracellular Ltp1 dephosphorylates PTEN on Y336 which results in elevated proteasomal degradation [ 44 ]. Reduced PTEN levels cause an increase in signaling through the PI3K-Akt pathway which converges on transcriptional upregulation of Regulator of Growth and Cell Cycle (RGCC) ( Figure 2 ).…”

Porphyromonas gingivalis Induces Increases in Branched-Chain Amino Acid Levels and Exacerbates Liver Injury Through livh/livk

“…Specifically, periodontitis, which is an inflammatory disease that is initiated by the dysbiosis of oral flora, is characterized by the destruction of alveolar bone and connective tissues around the teeth ( Liu et al., 2017b ; Lu et al., 2020 ; Hajishengallis and Lamont, 2021 ). It has also been suggested that Porphyromonas gingivalis , a gram-negative anaerobe, is the most important pathogenic bacterium in periodontitis ( Lamont et al., 2018 ; Liu et al., 2021 ). Furthermore, P. gingivalis possesses a plurality of virulence factors that invade periodontal tissues and subsequently enter blood circulation and disseminate into the whole body, increasing the risk of several systemic diseases, notably diabetes, cardiovascular diseases, rheumatoid arthritis, Alzheimer’s disease, and NAFLD ( Potempa et al., 2017 ; Nakahara et al., 2018 ; Mei et al., 2020 ; Fitzsimonds et al., 2021 ).…”