Altered Protein Interactions of the Endogenous Interactome of PTPIP51 towards MAPK Signaling

Modulation of ER-mitochondria tethering complex VAPB-PTPIP51: Novel therapeutic targets for aging-associated diseases

Aging is a gradual and irreversible natural process. With aging, the body experiences a functional decline, and the effects amplify the vulnerability to a range of age-related diseases, including neurodegenerative, cardiovascular, and metabolic diseases. Within the aging process, the morphology and function of mitochondria and the endoplasmic reticulum (ER) undergo alterations, particularly in the structure connecting these organelles known as mitochondria-associated membranes (MAMs). MAMs serve as vital intracellular signaling hubs, facilitating communication between the ER and mitochondria when regulating various cellular events, including calcium homeostasis, lipid metabolism, mitochondrial function, and apoptosis. The formation of MAMs is partly dependent on the interaction between the vesicle-associated membrane protein-associated protein-B (VAPB) and protein tyrosine phosphatase-interacting protein-51 (PTPIP51). Accumulating evidence has begun to elucidate the pivotal role of the VAPB-PTPIP51 tether in the initiation and progression of age-related diseases. In this study, we delineate the intricate structure and multifunctional role of the VAPB-PTPIP51 tether and discuss its profound implications in aging-associated diseases. Moreover, we provide a comprehensive overview of potential therapeutic interventions and pharmacological agents targeting the VAPB-PTPIP51-mediated MAMs, thereby offering a glimmer of hope in mitigating aging processes and treating age-related disorders.

Disruption of Mitochondrial-associated ER membranes by HIV-1 tat protein contributes to premature brain aging

INTRODUCTION

Mitochondrial-associated ER membranes (MAMs) control many cellular functions, including calcium and lipid exchange, intracellular trafficking, and mitochondrial biogenesis. The disruption of these functions contributes to neurocognitive disorders, such as spatial memory impairment and premature brain aging. Using neuronal cells, we demonstrated that HIV-1 Tat protein deregulates the mitochondria.

METHODS& RESULTS

To determine the mechanisms, we used a neuronal cell line and showed that Tat-induced changes in expression and interactions of both MAM-associated proteins and MAM tethering proteins. The addition of HIV-1 Tat protein alters expression levels of PTPIP51 and VAPB proteins in the MAM fraction but not the whole cell. Phosphorylation of PTPIP51 protein regulates its subcellular localization and function. We demonstrated that the Tat protein promotes PTPIP51 phosphorylation on tyrosine residues and prevents its binding to VAPB. Treatment of the cells with a kinase inhibitor restores the PTPIP51-VAPB interaction and overcomes the effect of Tat.

CONCLUSION

These results suggest that Tat disrupts the MAM, through the induction of PTPIP51 phosphorylation, leading to ROS accumulation, mitochondrial stress, and altered movement. Hence, we concluded that interfering in the MAM-associated cellular pathways contributes to spatial memory impairment and premature brain aging often observed in HIV-1-infected patients.

The Potential of Small Molecules to Modulate the Mitochondria–Endoplasmic Reticulum Interplay in Alzheimer’s Disease

Alzheimer’s disease (AD) is the most common neurodegenerative disease affecting a growing number of elderly individuals. No disease-modifying drugs have yet been identified despite over 30 years of research on the topic, showing the need for further research on this multifactorial disease. In addition to the accumulation of amyloid β-peptide (Aβ) and hyperphosphorylated tau (p-tau), several other alterations have been associated with AD such as calcium (Ca2+) signaling, glucose-, fatty acid-, cholesterol-, and phospholipid metabolism, inflammation, and mitochondrial dysfunction. Interestingly, all these processes have been associated with the mitochondria–endoplasmic reticulum (ER) contact site (MERCS) signaling hub. We and others have hypothesized that the dysregulated MERCS function may be one of the main pathogenic pathways driving AD pathology. Due to the variety of biological processes overseen at the MERCS, we believe that they constitute unique therapeutic targets to boost the neuronal function and recover neuronal homeostasis. Thus, developing molecules with the capacity to correct and/or modulate the MERCS interplay can unleash unique therapeutic opportunities for AD. The potential pharmacological intervention using MERCS modulators in different models of AD is currently under investigation. Here, we survey small molecules with the potential to modulate MERCS structures and functions and restore neuronal homeostasis in AD. We will focus on recently reported examples and provide an overview of the current challenges and future perspectives to develop MERCS modulators in the context of translational research.

PTPIP51 crosslinks the NFκB signaling and the MAPK pathway in SKBR3 cells

Aim:

PTPIP51 interacts with NFκB signaling at the RelA and IκB level. NFκB signaling is linked to the initiation, progression and metastasis of breast cancer. Her2-amplified breast cancer cells frequently display activation of the NFκB signaling. We aimed to clarify the effects of NFκB inhibition on the NFκB- and MAPK-related interactome of PTPIP51 and cell viability in HaCat cells and SKBR3 cells.

Results:

IKK-16 selectively reduced cell viability in SKBR3 cells. PDTC induced a formation of the Raf1/14-3-3/PTPIP51 complex in SKBR3 cells, indicating a shift of PTPIP51 into MAPK signaling.

Conclusion:

IKK-16 selectively inhibits cell viability of SKBR3 cells. In addition, PTPIP51 might serve as the mediator between NFκB signaling and the MAPK pathway in SKBR3.

Breast cancer is the most common cancerous disease among women. Prognosis and therapy of breast cancer depends on the expression of hormone and surface receptors such as Her2, which promote tumor growth and invasion via activation of downstream signaling pathways. NFκB signaling represents a downstream signaling pathway that can be activated by Her2. In this study, we demonstrated that inhibition of NFκB signaling with IKK-16 reduces cell viability in breast cancer cells with amplified Her2. Furthermore, we identified PTPIP51 as a potential mediator of crosstalks between the MAPK pathway and NFκB signaling. This signaling pathway could therefore be a target for future drug development.

Crosstalks of the PTPIP51 interactome revealed in Her2 amplified breast cancer cells by the novel small molecule LDC3/Dynarrestin

LDC3/Dynarrestin, an aminothiazole derivative, is a recently developed small molecule, which binds protein tyrosine phosphatase interacting protein 51 (PTPIP51). PTPIP51 interacts with various proteins regulating different signaling pathways leading to proliferation and migration. Her2 positive breast cancer cells (SKBR3) express high levels of PTPIP51. Therefore, we investigated the effects of LDC3/Dynarrestin on PTPIP51 and its interactome with 12 different proteins of various signal pathways including the interaction with dynein in SKBR3 cells. The localization and semi-quantification of PTPIP51 protein and the Tyr176 phosphorylated PTPIP51 protein were evaluated. Protein-protein-interactions were assessed by Duolink proximity ligation assays. Interactions and the activation of signal transduction hubs were examined with immunoblots. LDC3/Dynarrestin led to an increased PTPIP51 tyrosine 176 phosphorylation status while the overall amount of PTPIP51 remained unaffected. These findings are paralleled by an enhanced interaction of PTPIP51 with its crucial kinase c-Src and a reduced interaction with the counteracting phosphatase PTP1B. Furthermore, the treatment results in a significantly augmented interaction of PTPIP51/14-3-3β and PTPIP51/Raf1, the link to the MAPK pathway. Under the influence of LDC3/Dynarrestin, the activity of the MAPK pathway rose in a concentration-dependent manner as indicated by RTK assays and immunoblots. The novel small molecule stabilizes the RelA/IκB/PTPIP51 interactome and can abolish the effects caused by TNFα stimulation. Moreover, LDC3/Dynarrestin completely blocked the Akt signaling, which is essential for tumor growth. The data were compared to the recently described interactome of PTPIP51 in LDC3/Dynarrestin treated non-cancerous keratinocyte cells (HaCaT). Differences were identified exclusively for the mitochondrial-associated ER-membranes (MAM) interactions and phospho-regulation related interactome of PTPIP51.LDC3/Dynarrestin gives the opportunity/possibility to influence the MAPK signaling, NFkB signaling and probably calcium homeostasis in breast cancer cells by affecting the PTPIP51 interactome.

The Importance of the Right Framework: Mitogen-Activated Protein Kinase Pathway and the Scaffolding Protein PTPIP51

The protein tyrosine phosphatase interacting protein 51 (PTPIP51) regulates and interconnects signaling pathways, such as the mitogen-activated protein kinase (MAPK) pathway and an abundance of different others, e.g., Akt signaling, NF-κB signaling, and the communication between different cell organelles. PTPIP51 acts as a scaffold protein for signaling proteins, e.g., Raf-1, epidermal growth factor receptor (EGFR), human epidermal growth factor receptor 2 (Her2), as well as for other scaffold proteins, e.g., 14-3-3 proteins. These interactions are governed by the phosphorylation of serine and tyrosine residues of PTPIP51. The phosphorylation status is finely tuned by receptor tyrosine kinases (EGFR, Her2), non-receptor tyrosine kinases (c-Src) and the phosphatase protein tyrosine phosphatase 1B (PTP1B). This review addresses various diseases which display at least one alteration in these enzymes regulating PTPIP51-interactions. The objective of this review is to summarize the knowledge of the MAPK-related interactome of PTPIP51 for several tumor entities and metabolic disorders.