Placental expression of striatin & endothelial nitric oxide synthase in women with & without pre-eclampsia.

Background & objectives: Striatin is a multi-domain scaffolding protein essential for activating endothelial nitric oxide synthase (eNOS). However, its role in pre-eclampsia remains use explored. Hence, this study aimed to investigate the association between striatin and eNOS in regulating nitric oxide (NO) production in the placenta of women with and without pre-eclampsia. Methods: Forty pregnant women each without (controls) and with pre-eclampsia (cases) were enrolled in the study. Blood striatin and NO concentrations were detected by the ELISA. Protein expression of striatin, phosphorylated eNOS (peNOS), inducible NOS (iNOS) and phosphorylated NF-κB were measured in the placental tissues by Western blot. Twenty four hour urinary protein and serum urea, uric acid and creatinine were analyzed as an autoanalyzer. Placental histology was analyzed by haematoxylin and eosin staining. Results: Compared to normotensive pregnant women, the levels of serum NO and striatin were decreased in pre-eclamptic women. The protein expression of striatin and peNOS was significantly reduced (P<0.05) while p65NF-κB and iNOS were upregulated considerably (P<0.05) in the placenta of cases compared to controls. Interpretation & conclusions: Our results show for the first time that decreased striatin expression was associated with decreased peNOS protein expression in the placental tissue of pre-eclamptic women. Interestingly, no significant difference was found in blood striatin or NO levels between controls and cases. Thus, therapies that improve placental striatin expression are attractive possibilities, both for prevention as well as treatment of endothelial dysfunction in pre-eclampsia.

STRIPAK-PP2A regulates Hippo-Yorkie signaling to suppress retinal fate in the Drosophila eye disc peripodial epithelium.

The specification of organs, tissues and cell types results from cell fate restrictions enacted by nuclear transcription factors under the control of conserved signaling pathways. The progenitor epithelium of the Drosophila compound eye, the eye imaginal disc, is a premier model for the study of such processes. Early in development, apposing cells of the eye disc are established as either retinal progenitors or support cells of the peripodial epithelium (PE), in a process whose genetic and mechanistic determinants are poorly understood. We have identified protein phosphatase 2A (PP2A), and specifically a STRIPAK-PP2A complex that includes the scaffolding and substrate-specificity components Cka, Strip and SLMAP, as a critical player in the retina-PE fate choice. We show that these factors suppress ectopic retina formation in the presumptive PE and do so via the Hippo signaling axis. STRIPAK-PP2A negatively regulates Hippo kinase, and consequently its substrate Warts, to release the transcriptional co-activator Yorkie into the nucleus. Thus, a modular higher-order PP2A complex refines the activity of this general phosphatase to act in a precise specification of cell fate.

The profile of expression of the scaffold protein SG2NA(s) differs between cancer types and its interactome in normal vis-a-vis breast tumor tissues suggests its wide roles in regulating multiple cellular pathways.

Striatin and SG2NA are scaffold proteins that form signaling complexes called STRIPAK. It has been associated with developmental abnormalities, cancer, and several other diseases. Our earlier studies have shown that SG2NA forms a complex with the cancer-associated protein DJ-1 and the signaling kinase Akt, promoting cancer cell survival. In the present study, we used bioinformatics analyses to confirm the existence of two isoforms of human SG2NA, i.e., 78 and 87 kDas. In addition, several smaller isoforms like 35 kDa were also seen in western blot analyses of human cell lysates. The expression of these isoforms varies between different cancer cell lines of human origin. Also, the protein levels do not corroborate with its transcript levels, suggesting a complex regulation of its expression. In breast tumor tissues, the expression of the 35 and 78 kDa isoforms was higher as compared to the adjacent normal tissues, while the 87 kDa isoform was found in the breast tumor tissues only. With the progression of stages of breast cancer, while the expression of 78 kDa isoform decreased, 87 kDa became undetectable. In co-immunoprecipitation assays, the profile of the SG2NA interactome in breast tumors vis-à-vis adjacent normal breast tissues showed hundreds of common proteins. Also, some proteins were interacted with SG2NA in breast tumor tissues only. We conclude that SG2NA is involved in diverse cellular pathways and has roles in cellular reprogramming during tumorigenesis of the breast.

Subcellular dynamics of variants of SG2NA in NIH3T3 fibroblasts.

SG2NA, a WD40 repeat protein of the Striatin subfamily, has four splicing and one messenger RNA edit variants. It is fast emerging as a scaffold for multimeric signaling complexes with roles in tissue development and disease. The green fluorescent protein (GFP)-tagged variants of SG2NA were ectopically expressed in NIH3T3 cells and their modulation by serum and GSK3ß-ERK signaling were monitored. The 87, 78, and 35 kDa variants showed a biphasic modulation by serum till 24 h but the 52 kDa variant remained largely unresponsive. Inhibition of phosphatases by okadaic acid increased the levels of the endogenous 78 kDa and the ectopically expressed GFP-tagged 87 and 78 kDa SG2NAs. Contrastingly, okadaic acid treatment reduced the level of GFP-tagged 35 kDa SG2NA, suggesting differential modes of their stability through phosphorylation-dephosphorylation. The inhibition of GSK3ß by LiCl showed a gradual decrease in the levels of 78 kDa. In the case of the other variants viz, GFP-tagged 35, 52, and 87 kDa, inhibition of GSK3ß caused an initial increase followed by a decrease with a subtle difference in kinetics and intensities. Similar results were also seen upon inhibition of GSK3ß by small interfering RNA. All the variants showed an increase followed by a decrease upon inhibition of extracellular-signal-regulated-kinase (ERK). These variants are localized in the plasma membrane, endoplasmic reticulum, mitochondria, and the nucleus with different propensities and no discernable subcellular distribution was seen upon stimulation by serum and the inhibition of phosphatases, GSK3ß, and ERK. Taken together, the variants of SG2NA are modulated by the kinase-phosphatase network in a similar but characteristic manner.

Striatin-1 is a B subunit of protein phosphatase PP2A that regulates dendritic arborization and spine development in striatal neurons.

Striatin-1, a subunit of the serine/threonine phosphatase PP2A, is preferentially expressed in neurons in the striatum. As a member of the striatin family of B subunits, striatin-1 is a core component together with PP2A of a multiprotein complex called STRIPAK, the striatin-interacting phosphatase and kinase complex. Little is known about the function of striatin-1 or the STRIPAK complex in the mammalian striatum. Here, we identify a selective role for striatin-1 in striatal neuron maturation. Using a small hairpin RNA (shRNA) knockdown approach in primary striatal neuronal cultures, we determined that reduced expression of striatin-1 results in increased dendritic complexity and an increased density of dendritic spines, classified as stubby spines. The dendritic phenotype was rescued by co-expression of a striatin-1 mutant construct insensitive to the knockdown shRNA but was not rescued by co-expression of PP2A- or Mob3-binding deficient striatin-1 constructs. Reduction of striatin-1 did not result in deficits in neuronal connectivity in this knockdown model, as we observed no abnormalities in synapse formation or in spontaneous excitatory postsynaptic currents. Thus, this study suggests that striatin-1 is a regulator of neuronal development in striatal neurons.

STRIPAK, a highly conserved signaling complex, controls multiple eukaryotic cellular and developmental processes and is linked with human diseases.

The striatin-interacting phosphatases and kinases (STRIPAK) complex is evolutionary highly conserved and has been structurally and functionally described in diverse lower and higher eukaryotes. In recent years, this complex has been biochemically characterized better and further analyses in different model systems have shown that it is also involved in numerous cellular and developmental processes in eukaryotic organisms. Further recent results have shown that the STRIPAK complex functions as a macromolecular assembly communicating through physical interaction with other conserved signaling protein complexes to constitute larger dynamic protein networks. Here, we will provide a comprehensive and up-to-date overview of the architecture, function and regulation of the STRIPAK complex and discuss key issues and future perspectives, linked with human diseases, which may form the basis of further research endeavors in this area. In particular, the investigation of bi-directional interactions between STRIPAK and other signaling pathways should elucidate upstream regulators and downstream targets as fundamental parts of a complex cellular network.

SLMAP-3 is downregulated in human dilated ventricles and its overexpression promotes cardiomyocyte response to adrenergic stimuli by increasing intracellular calcium.

Structural dilation of cardiomyocytes (CMs) imposes a decline in cardiac performance that precipitates cardiac failure and sudden death. Since membrane proteins are implicated in dilated cardiomyopathy and heart failure, we evaluated the expression of the sarcolemmal membrane-associated protein (SLMAP) in dilated cardiomyopathy and its effect on CM contraction. We found that all 3 SLMAP isoforms (SLMAP-1, -2, and -3) are expressed in CMs and are downregulated in human dilated ventricles. Knockdown of SLMAPs in cultured CMs transduced with recombinant adeno-associated viral particles releasing SLMAP-shRNA precipitated reduced spontaneous contractile rate that was not fully recovered in SLMAP-depleted CMs challenged with isoproterenol (ISO), thus phenotypically mimicking heart failure performance. Interestingly, the overexpression of the SLMAP-3 full-length isoform induced a positive chronotropic effect in CMs that was more pronounced in response to ISO insult (vs. ISO-treated naïve CMs). Confocal live imaging showed that H9c2 cardiac myoblasts overexpressing SLMAP-3 exhibit a higher intracellular calcium transient peak when treated with ISO (vs. ISO-treated cells carrying a control adeno-associated viral particle). Proteomics revealed that SLMAP-3 interacts with the regulator of CM contraction, striatin. Collectively, our data demonstrate that SLMAP-3 is a novel regulator of CM contraction rate and their response to adrenergic stimuli. Loss of SLMAPs phenotypically mimics cardiac failure and crystallizes SLMAPs as predictive of dilated cardiomyopathy and heart failure.

FvSTR1, a striatin orthologue in Fusarium virguliforme, is required for asexual development and virulence.

The soil-borne fungus Fusarium virguliforme causes sudden death syndrome (SDS), one of the most devastating diseases of soybean in North and South America. Despite the importance of SDS, a clear understanding of the fungal pathogenicity factors that affect the development of this disease is still lacking. We have identified FvSTR1, a F. virguliforme gene, which encodes a protein similar to a family of striatin proteins previously reported to regulate signalling pathways, cell differentiation, conidiation, sexual development, and virulence in filamentous fungi. Striatins are multi-domain proteins that serve as scaffolding units in the striatin-interacting phosphatase and kinase (STRIPAK) complex in fungi and animals. To address the function of a striatin homologue in F. virguliforme, FvSTR1 was disrupted and functionally characterized using a gene knock out strategy. The resulting Fvstr1 mutants were largely impaired in conidiation and pigmentation, and displayed defective conidia and conidiophore morphology compared to the wild-type and ectopic transformants. Greenhouse virulence assays revealed that the disruption of FvSTR1 resulted in complete loss of virulence in F. virguliforme. Microtome studies using fluorescence microscopy showed that the Fvstr1 mutants were defective in their ability to colonize the vascular system. The Fvstr1 mutants also showed a reduced transcript level of genes involved in asexual reproduction and in the production of secondary metabolites. These results suggest that FvSTR1 has a critical role in asexual development and virulence in F. virguliforme.

Cardiac striatin interacts with caveolin-3 and calmodulin in a calcium sensitive manner and regulates cardiomyocyte spontaneous contraction rate.

Impaired cardiomyocyte contraction rate is detrimental to cardiac function and often lethal. Despite advancements in the field, there is a paucity of information regarding the coordination of molecules implicated in regulating the heart rate. Striatin (STRN) is a dynamic protein with binding domains to calmodulin (CaM) and caveolin (Cav), both of which are regulators of myocardial function. However, its role in cardiomyocyte contraction is not yet determined. Herein, we show that STRN is expressed in cardiomyocytes and is more abundant in atrial myocardium than in ventricles. Cardiac expression of STRN (protein and mRNA) was developmentally regulated with the highest expression being at neonatal stage (day one) and the lowest in adult rats (13 weeks). CaM pulldown assay indicated that the interaction of cardiac STRN with CaM and caveolin-3 (Cav-3) was calcium sensitive. Interestingly, the overexpression of STRN induced an increase (∼2-fold) in the rate of the spontaneous contraction of cultured cardiomyocytes, while the knockdown of STRN reduced their contraction rate (∼40%). The expression level of STRN was inversely proportional to the interaction of Cav-3 with the CaM/STRN complex. Collectively, our data delineate a novel role for STRN in regulating cardiomyocyte spontaneous contraction rate and the dynamics of the STRN/Cav-3/CaM complex.

Protein phosphatase PP2A - a novel interacting partner of carnitine transporter OCTN2 (SLC22A5) in rat astrocytes.

l-Carnitine is essential for translocation of fatty acids for their mitochondrial ß-oxidation, a process shown in the brain to take place in astrocytes. Organic cation and carnitine plasma membrane transporter OCTN2 (SLC22A5) is present in astrocytes. OCTN2 activity and localization were previously shown to be regulated by protein kinase C (PKC), although no phosphorylation of the transporter was detected. In this study, mass spectrometry was used to identify rOctn2-interacting partners in astrocytes: several cytoskeletal, ribosomal, mitochondrial, heat-shock proteins, as well as proteins involved in trafficking and signaling pathways. The analysis of signaling proteins shows that Octn2 co-precipitated with PP2A phosphatase catalytical (C) and structural (A) subunits, and with its regulatory B"' subunits - striatin, SG2NA, and zinedin. The Octn2/PP2A complex is mainly detected in endoplasmic reticulum. PKC activation increases both, carnitine transport and, as shown by immunofluorescence and surface biotinylation, transporter presence in plasma membrane. It also results in phosphorylation of SG2NA, zinedin, and catalytical subunit, although co-precipitation, immunocytochemistry, and proximity ligation assay experiments showed that only the amount of SG2NA decreased in the complex with Octn2. PP2A inhibition with okadaic acid does not lead to Octn2 phosphorylation; however, it abolishes observed effects of PKC activation. We postulate that PKC phosphorylates SG2NA, resulting in its dissociation from the complex and transfer of Octn2 to the plasma membrane, leading to increased transporter activity. The observed interaction could affect brain functioning in vivo, both in fatty acid metabolism and in control of carnitine homeostasis, known to change in certain brain pathologies.

The composition and function of the striatin-interacting phosphatases and kinases (STRIPAK) complex in fungi.

The striatin-interacting phosphatases and kinases (STRIPAK) complex is a highly conserved eukaryotic protein complex that was recently described for diverse animal and fungal species. Here, we summarize our current knowledge about the composition and function of the STRIPAK complex from the ascomycete Sordaria macrospora, which we discovered by investigating sexually sterile mutants (pro), having a defect in fruiting body development. Mass spectrometry and yeast two-hybrid analysis defined core subunits of the STRIPAK complex, which have structural homologs in animal and other fungal organisms. These subunits (and their mammalian homologs) are PRO11 (striatin), PRO22 (STRIP1/2), SmMOB3 (Mob3), PRO45 (SLMAP), and PP2AA, the structural, and PP2Ac, the catalytic subunits of protein phosphatase 2A (PP2A). Beside fruiting body formation, the STRIPAK complex controls vegetative growth and hyphal fusion in S. macrospora. Although the contribution of single subunits to diverse cellular and developmental processes is not yet fully understood, functional analysis has already shown that mammalian homologs are able to substitute the function of distinct fungal STRIPAK subunits. This underscores the view that fungal model organisms serve as useful tools to get a molecular insight into cellular and developmental processes of eukaryotes in general. Future work will unravel the precise localization of single subunits within the cell and decipher their STRIPAK-related and STRIPAK-independent functions. Finally, evidence is accumulating that there is a crosstalk between STRIPAK and various signaling pathways, suggesting that eukaryotic development is dependent on STRIPAK signaling.

Striatins contain a noncanonical coiled coil that binds protein phosphatase 2A A subunit to form a 2:2 heterotetrameric core of striatin-interacting phosphatase and kinase (STRIPAK) complex.

The protein phosphatase 2A (PP2A) and kinases such as germinal center kinase III (GCKIII) can interact with striatins to form a supramolecular complex called striatin-interacting phosphatase and kinase (STRIPAK) complex. Despite the fact that the STRIPAK complex regulates multiple cellular events, it remains only partially understood how this complex itself is assembled and regulated for differential biological functions. Our recent work revealed the activation mechanism of GCKIIIs by MO25, as well as how GCKIIIs heterodimerize with CCM3, a molecular bridge between GCKIII and striatins. Here we dissect the structural features of the coiled coil domain of striatin 3, a novel type of PP2A regulatory subunit that functions as a scaffold for the assembly of the STRIPAK complex. We have determined the crystal structure of a selenomethionine-labeled striatin 3 coiled coil domain, which shows it to assume a parallel dimeric but asymmetric conformation containing a large bend. This result combined with a number of biophysical analyses provide evidence that the coiled coil domain of striatin 3 and the PP2A A subunit form a stable core complex with a 2:2 stoichiometry. Structure-based mutational studies reveal that homodimerization of striatin 3 is essential for its interaction with PP2A and therefore assembly of the STRIPAK complex. Wild-type striatin 3 but not the mutants defective in PP2A binding strongly suppresses apoptosis of Jurkat cells induced by the GCKIII kinase MST3, most likely through a mechanism in which striatin recruits PP2A to negatively regulate the activation of MST3. Collectively, our work provides structural insights into the organization of the STRIPAK complex and will facilitate further functional studies.

SG2NA enhances cancer cell survival by stabilizing DJ-1 and thus activating Akt.

SG2NA in association with striatin and zinedin forms a striatin family of WD-40 repeat proteins. This family of proteins functions as scaffold in different signal transduction pathways. They also act as a regulatory subunit of protein phosphatase 2A. We have shown that SG2NA which evolved first in the metazoan evolution among the striatin family members expresses different isoforms generated out of alternative splicing. We have also shown that SG2NA protects cells from oxidative stress by recruiting DJ-1 and Akt to mitochondria and membrane in the post-mitotic neuronal cells. DJ-1 is both cancer and Parkinson's disease related protein. In the present study we have shown that SG2NA protects DJ-1 from proteasomal degradation in cancer cells. Hence, downregulation of SG2NA reduces DJ-1/Akt colocalization in cancer cells resulting in the reduction of anchorage dependent and independent growth. Thus SG2NA enhances cancer cell survival. Reactive oxygen species enhances SG2NA, DJ-1 and Akt trimerization. Removal of the reactive oxygen species by N-acetyl-cysteine thus reduces cancer cell growth.

17ß-Estradiol inhibits vascular smooth muscle cell migration via up-regulation of striatin protein.

Striatin, an estrogen receptor (ER)-interacting protein, plays an important role in estrogen's nongenomic actions in vascular endothelial cells. However, the role of striatin in VSMCs is unknown. Here, we investigated the role of striatin in estrogen-regulated VSMCs migration. 17ß-Estradiol (E2) at 10 nM largely inhibited VSMCs migration, which was reversed by the silencing of striatin expression. E2 increased striatin protein expression in a dose- and time-dependent manner. ERα agonist PPT, but not ERß agonist DPN, mimicked the regulatory effect of E2. The regulatory effect of E2 on striatin protein expression was blocked by the pure ER antagonist ICI 182,780 or the mitogen-activated protein kinase inhibitor PD98059, but not by the phosphatidylinositol-3 kinase inhibitor wortmannin or Src inhibitor PP2, suggesting that E2 increased striatin protein expression via extracellular-signal regulated kinase 1/2 (ERK1/2). E2 resulted in phosphorylation of ERK1/2 in a time-dependent manner. The silencing of ERK1/2 largely abolished E2-enhanced striatin expression. Finally, the inhibitory effect of E2 on VSMC migration was reversed by ICI 182,780 or PD98059. Taken together, our results indicate that E2 inhibits VSMC migration by increasing striatin expression via ERα to ERK1/2 pathway, which maybe helpful to understand estrogen's anti-atherogenic effect in VSMCs.

Silencing of STRN4 suppresses the malignant characteristics of cancer cells.

The striatin family of proteins, comprising STRN, STRN3 and STRN4, are multidomain-containing proteins that associate with additional proteins to form a large protein complex. We previously reported that STRN4 directly associated with protein kinases, such as MINK1, TNIK and MAP4K4, which are associated with tumor suppression or tumor progression. However, it remains unclear whether STRN4 is associated with tumor progression. In this report, we examined the role that STRN4 plays in cancer malignancy. We show that depletion of STRN4 suppresses proliferation, migration, invasion and the anchorage-independent growth of cancer cells. In addition, STRN4 knockdown increases the sensitivity of pancreatic cancer cells to gemcitabine. Finally, we show that STRN4 knockdown suppresses the proliferation and metastasis of cancer cells in mice. Our results demonstrate a possible role of STRN4 in tumor progression.

Striatin knock out induces a gain of function of INa and impaired Ca2+ handling in mESC-derived cardiomyocytes.

AIM: Striatin (Strn) is a scaffold protein expressed in cardiomyocytes (CMs) and alteration of its expression are described in various cardiac diseases. However, the alteration underlying its pathogenicity have been poorly investigated. METHODS: We studied the role(s) of cardiac Strn gene (STRN) by comparing the functional properties of CMs, generated from Strn-KO and isogenic WT mouse embryonic stem cell lines. RESULTS: The spontaneous beating rate of Strn-KO CMs was faster than WT cells, and this correlated with a larger fast INa conductance and no changes in If. Paced (2-8 Hz) Strn-KO CMs showed prolonged action potential (AP) duration in comparison with WT CMs and this was not associated with changes in ICaL and IKr. Motion video tracking analysis highlighted an altered contraction in Strn-KO CMs; this was associated with a global increase in intracellular Ca2+, caused by an enhanced late Na+ current density (INaL) and a reduced Na+/Ca2+ exchanger (NCX) activity and expression. Immunofluorescence analysis confirmed the higher Na+ channel expression and a more dynamic microtubule network in Strn-KO CMs than in WT. Indeed, incubation of Strn-KO CMs with the microtubule stabilizer taxol, induced a rescue (downregulation) of INa conductance toward WT levels. CONCLUSION: Loss of STRN alters CMs electrical and contractile profiles and affects cell functionality by a disarrangement of Strn-related multi-protein complexes. This leads to impaired microtubules dynamics and Na+ channels trafficking to the plasma membrane, causing a global Na+ and Ca2+ enhancement.

Mitf, with Yki and STRIPAK-PP2A, is a key determinant of form and fate in the progenitor epithelium of the Drosophila eye.

The Microphthalmia-associated Transcription Factor (MITF) governs numerous cellular and developmental processes. In mice, it promotes specification and differentiation of the retinal pigmented epithelium (RPE), and in humans, some mutations in MITF induce congenital eye malformations. Herein, we explore the function and regulation of Mitf in Drosophila eye development and uncover two roles. We find that knockdown of Mitf results in retinal displacement (RDis), a phenotype associated with abnormal eye formation. Mitf functions in the peripodial epithelium (PE), a retinal support tissue akin to the RPE, to suppress RDis, via the Hippo pathway effector Yorkie (Yki). Yki physically interacts with Mitf and can modify its transcriptional activity in vitro. Severe loss of Mitf, instead, results in the de-repression of retinogenesis in the PE, precluding its development. This activity of Mitf requires the protein phosphatase 2 A holoenzyme STRIPAK-PP2A, but not Yki; Mitf transcriptional activity is potentiated by STRIPAK-PP2A in vitro and in vivo. Knockdown of STRIPAK-PP2A results in cytoplasmic retention of Mitf in vivo and in its decreased stability in vitro, highlighting two potential mechanisms for the control of Mitf function by STRIPAK-PP2A. Thus, Mitf functions in a context-dependent manner as a key determinant of form and fate in the Drosophila eye progenitor epithelium.

Striatin family proteins: The neglected scaffolds.

The Striatin family of proteins constitutes Striatin, SG2NA, and Zinedin. Members of this family of proteins act as a signaling scaffold due to the presence of multiple protein-protein interaction domains. At least two members of this family, namely Zinedin and SG2NA, have a proven role in cancer cell proliferation. SG2NA, the second member of this family, undergoes alternative splicing and gives rise to several isoforms which are differentially regulated in a tissue-dependent manner. SG2NA evolved earlier than the other two members of the family, and SG2NA undergoes not only alternative splicing but also other posttranscriptional gene regulation. Striatin also undergoes alternative splicing, and as a result, it gives rise to multiple isoforms. It has been shown that this family of proteins plays a significant role in estrogen signaling, neuroprotection, cancer as well as in cell cycle regulation. Members of the striatin family form a complex network of signaling hubs with different kinases and phosphatases, and other signaling proteins named STRIPAK. Here, in the present manuscript, we thoroughly reviewed the findings on striatin family members to elaborate on the overall structural and functional idea of this family of proteins. We also commented on the involvement of these proteins in STRIPAK complexes and their functional relevance.

STRIP2 motivates non-small cell lung cancer progression by modulating the TMBIM6 stability through IGF2BP3 dependent.

BACKGROUND: Striatin interacting protein 2 (STRIP2) is a core component of the striatin-interacting phosphatase and kinase (STRIPAK) complexes, which is involved in tumor initiation and progression via the regulation of cell contractile and metastasis. However, the underlying molecular mechanisms of STRIP2 in non-small cell lung cancer (NSCLC) progression remain largely unknown. METHODS: The expressions of STRIP2 and IGF2BP3 in human NSCLC specimens and NSCLC cell lines were detected using quantitative RT-PCR, western blotting, and immunohistochemistry (IHC) analyses. The roles and molecular mechanisms of STRIP2 in promoting NSCLC progression were investigated in vitro and in vivo. RESULTS: Here, we found that STRIP2 expression was significantly elevated in NSCLC tissues and high STRIP2 expression was associated with a poor prognosis. Knockdown of STRIP2 suppressed tumor growth and metastasis in vitro and in vivo, while STRIP2 overexpression obtained the opposite effect. Mechanistically, P300/CBP-mediated H3K27 acetylation activation in the promoter of STRIP2 induced STRIP2 transcription, which interacted with insulin-like growth factor 2 mRNA-binding protein 3 (IGF2BP3) and upregulated IGF2BP3 transcription. In addition, STRIP2-IGF2BP3 axis stimulated m6A modification of TMBIM6 mRNA and enhanced TMBIM6 stability. Consequently, TMBIM6 involved NSCLC cell proliferation, migration and invasion dependent on STRIP2 and IGF2BP3. In NSCLC patients, high co-expression of STRIP2, IGF2BP3 and TMBIM6 was associated with poor outcomes. CONCLUSIONS: Our findings indicate that STRIP2 interacts with IGF2BP3 to regulate TMBIM6 mRNA stability in an m6A-dependent manner and may represent a potential prognostic biomarker and therapeutic target for NSCLC.

Cellular Impacts of Striatins and the STRIPAK Complex and Their Roles in the Development and Metastasis in Clinical Cancers (Review).

Striatins (STRNs) are generally considered to be cytoplasmic proteins, with lower expression observed in the nucleus and at cell-cell contact regions. Together with protein phosphatase 2A (PP2A), STRNs form the core region of striatin-interacting phosphatase and kinase (STRIPAK) complexes through the coiled-coil region of STRN proteins, which is crucial for substrate recruitment. Over the past two decades, there has been an increasing amount of research into the biological and cellular functions of STRIPAK members. STRNs and the constituent members of the STRIPAK complex have been found to regulate several cellular functions, such as cell cycle control, cell growth, and motility. Dysregulation of these cellular events is associated with cancer development. Importantly, their roles in cancer cells and clinical cancers are becoming recognised, with several STRIPAK components found to have elevated expression in cancerous tissues compared to healthy tissues. These molecules exhibit significant diagnostic and prognostic value across different cancer types and in metastatic progression. The present review comprehensively summarises and discusses the current knowledge of STRNs and core STRIPAK members, in cancer malignancy, from both cellular and clinical perspectives.