SRPK1: a cisplatin sensitive protein expressed in retinoblastoma

Functions of SRPK, CLK and DYRK kinases in stem cells, development, and human developmental disorders

Human developmental disorders encompass a wide range of debilitating physical conditions and intellectual disabilities. Perturbation of protein kinase signalling underlies the development of some of these disorders. For example, disrupted SRPK signalling is associated with intellectual disabilities, and the gene dosage of DYRKs can dictate the pathology of disorders including Down's syndrome. Here, we review the emerging roles of the CMGC kinase families SRPK, CLK, DYRK, and sub-family HIPK during embryonic development and in developmental disorders. In particular, SRPK, CLK, and DYRK kinase families have key roles in developmental signalling and stem cell regulation, and can co-ordinate neuronal development and function. Genetic studies in model organisms reveal critical phenotypes including embryonic lethality, sterility, musculoskeletal errors, and most notably, altered neurological behaviours arising from defects of the neuroectoderm and altered neuronal signalling. Further unpicking the mechanisms of specific kinases using human stem cell models of neuronal differentiation and function will improve our understanding of human developmental disorders and may provide avenues for therapeutic strategies.

Targeting pre-mRNA splicing in cancers: roles, inhibitors, and therapeutic opportunities

Accumulating evidence has indicated that pre-mRNA splicing plays critical roles in a variety of physiological processes, including development of multiple diseases. In particular, alternative splicing is profoundly involved in cancer progression through abnormal expression or mutation of splicing factors. Small-molecule splicing modulators have recently attracted considerable attention as a novel class of cancer therapeutics, and several splicing modulators are currently being developed for the treatment of patients with various cancers and are in the clinical trial stage. Novel molecular mechanisms modulating alternative splicing have proven to be effective for treating cancer cells resistant to conventional anticancer drugs. Furthermore, molecular mechanism-based combination strategies and patient stratification strategies for cancer treatment targeting pre-mRNA splicing must be considered for cancer therapy in the future. This review summarizes recent progress in the relationship between druggable splicing-related molecules and cancer, highlights small-molecule splicing modulators, and discusses future perspectives of splicing modulation for personalized and combination therapies in cancer treatment.

Good Cop, Bad Cop: The Different Roles of SRPKs

SR Protein Kinases (SRPKs), discovered approximately 30 years ago, are widely known as splice factor kinases due to their decisive involvement in the regulation of various steps of mRNA splicing. However, they were also shown to regulate diverse cellular activities by phosphorylation of serine residues residing in serine-arginine/arginine-serine dipeptide motifs. Over the last decade, SRPK1 has been reported as both tumor suppressor and promoter, depending on the cellular context and has been implicated in both chemotherapy sensitivity and resistance. Moreover, SRPK2 has been reported to exhibit contradictory functions in different cell contexts promoting either apoptosis or tumor growth. The aim of the current review is to broaden and deepen our understanding of the SRPK function focusing on the subcellular localization of the kinases. There is ample evidence that the balance between cytoplasmic and nuclear SRPK levels is tightly regulated and determines cell response to external signals. Specific cell states coupled to kinase levels, spatial specific interactions with substrates but also changes in the extent of phosphorylation that allow SRPKs to exhibit a rheostat-like control on their substrates, could decide the proliferative or antiproliferative role of SRPKs.

Serine-Arginine Protein Kinase 1 (SRPK1): a systematic review of its multimodal role in oncogenesis

Alternative splicing is implicated in each of the hallmarks of cancer, and is mechanised by various splicing factors. Serine-Arginine Protein Kinase 1 (SRPK1) is an enzyme which moderates the activity of splicing factors rich in serine/arginine domains. Here we review SRPK1’s relationship with various cancers by performing a systematic review of all relevant published data. Elevated SRPK1 expression correlates with advanced disease stage and poor survival in many epithelial derived cancers. Numerous pre-clinical studies investigating a host of different tumour types; have found increased SRPK1 expression to be associated with proliferation, invasion, migration and apoptosis in vitro as well as tumour growth, tumourigenicity and metastasis in vivo. Aberrant SRPK1 expression is implicated in various signalling pathways associated with oncogenesis, a number of which, such as the PI3K/AKT, NF-КB and TGF-Beta pathway, are implicated in multiple different cancers. SRPK1-targeting micro RNAs have been identified in a number of studies and shown to have an important role in regulating SRPK1 activity. SRPK1 expression is also closely related to the response of various tumours to platinum-based chemotherapeutic agents. Future clinical applications will likely focus on the role of SRPK1 as a biomarker of treatment resistance and the potential role of its inhibition.

Increased expression of SRPK1 (serine/arginine-rich protein-specific kinase 1) is associated with progression and unfavorable prognosis in cervical squamous cell carcinoma

Previous studies suggest that SRPK1 (serine/arginine-rich protein-specific kinase 1) is involved in tumorigenesis and closely related to unfavorable outcomes. However, its expression pattern in cervical squamous cell carcinoma (CESC) remains uncovered. In this study, we initially investigated the clinical significance and function of SRPK1 in human CESC. Data mining and analysis on SRPK1 mRNA expression in CESC samples were conducted using TCGA database, which indicated that SRPK1 mRNA was significantly upregulated in CESC samples. Protein expression of SRPK1 was tested by immunohistochemistry in a retrospective cohort (n = 122), revealing a higher SRPK1 protein abundance in CESC specimens whose aberrant up-regulation was obviously related to worse survival. Cox proportional hazards regression analysis further confirmed the role of SRPK1 as an independent prognostic factor of CESC. Cellular experiments validated that SRPK1 may function through enhancing CESC proliferation, migration, and invasion. In conclusion, aberrant up-regulation of SRPK1 is remarkably related to progression and unfavorable prognosis of CESC, which can serve as a novel prognostic biomarker and therapeutic target for CESC.

Oncogenic dysregulation of pre-mRNA processing by protein kinases: challenges and therapeutic opportunities

Alternative splicing and polyadenylation represent two major steps in pre-mRNA-processing, which ensure proper gene expression and diversification of human transcriptomes. Deregulation of these processes contributes to oncogenic programmes involved in the onset, progression and evolution of human cancers, which often result in the acquisition of resistance to existing therapies. On the other hand, cancer cells frequently increase their transcriptional rate and develop a transcriptional addiction, which imposes a high stress on the pre-mRNA-processing machinery and establishes a therapeutically exploitable vulnerability. A prominent role in fine-tuning pre-mRNA-processing mechanisms is played by three main families of protein kinases: serine arginine protein kinase (SRPK), CDC-like kinase (CLK) and cyclin-dependent kinase (CDK). These kinases phosphorylate the RNA polymerase, splicing factors and regulatory proteins involved in cleavage and polyadenylation of the nascent transcripts. The activity of SRPKs, CLKs and CDKs can be altered in cancer cells, and their inhibition was shown to exert anticancer effects. In this review, we describe key findings that have been reported on these topics and discuss challenges and opportunities of developing therapeutic approaches targeting splicing factor kinases.

SRPK1/AKT axis promotes oxaliplatin-induced anti-apoptosis via NF-κB activation in colon cancer

Background

Colorectal cancer is the third most common diagnosis. Oxaliplatin is used as first-line treatment of colon cancer. However, oxaliplatin resistance greatly reduces its therapeutic effect. SRPK1 involves in pre-mRNA splicing and tumorigenesis. How SRPK1 mediates drug resistance in colon cancer is unknown.

Methods

The expression of SRPK1 was analyzed in the TCGA and the CPTAC pan-cancer samples and detected in colon cancer cell lines and tissues by IHC and western blot. The MTT and TUNEL assay were used to verify the anti-apoptosis ability of colon cancer cell. The activation of NF-κB was determined by luciferase assay and qRT-PCR. AKT, IKK, IκB and their phosphorylation level were verified by western blot.

Results

We found that SRPK1 expression was the second highest in TCGA and the CPTAC pan-cancer samples. The mRNA and protein levels of SRPK1 were increased in tissues from patients with colon cancer. SRPK1 was associated with clinical stage and TNM classifications in 148 cases of colon cancer patients. High SRPK1 levels correlated with poor prognosis (p < 0.001). SRPK1 overexpression enhanced the anti-apoptosis ability of colon cancer cells, whereas SRPK1 silencing had the opposite effect under oxaliplatin treatment. Mechanistically, SRPK1 enhances IKK kinase and IκB phosphorylation to promote NF-κB nuclear translocation to confer oxaliplatin resistance.

Conclusions

Our findings suggest that SRPK1 participates in colon cancer progression and enhances the anti-apoptosis capacity to induce drug resistance in colon cancer cells via NF-κB pathway activation, and thus might be a potential pharmaceutically target for colon cancer treatment.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12967-021-02954-8.

Nuclear Translocation of SRPKs Is Associated with 5-FU and Cisplatin Sensitivity in HeLa and T24 Cells

Serine/arginine protein kinases (SRPKs) phosphorylate Arg/Ser dipeptide-containing proteins that play crucial roles in a broad spectrum of basic cellular processes. The existence of a large internal spacer sequence that separates the bipartite kinase catalytic core and anchors the kinases in the cytoplasm is a unique structural feature of SRPKs. Here, we report that exposure of HeLa and T24 cells to DNA damage inducers triggers the nuclear translocation of SRPK1 and SRPK2. Furthermore, we show that nuclear SRPKs did not protect from, but on the contrary, mediated the cytotoxic effects of genotoxic agents, such as 5-fluorouracil (5-FU) and cisplatin. Confirming previous data showing that the kinase activity is essential for the entry of SRPKs into the nucleus, SRPIN340, a selective SRPK1/2 inhibitor, blocked the nuclear accumulation of the kinases, thus diminishing the cytotoxic effects of the drugs. ATR/ATM-dependent phosphorylation of threonine 326 and serine 408 in the spacer domain of SRPK1 was essential for the redistribution of the kinase to the nucleus. Substitution of either of these two residues to alanine or inhibition of ATR/ATM kinase activity abolished nuclear localization of SRPK1 and conferred tolerance to 5-FU treatment. These findings suggest that SRPKs may play an important role in linking cellular signaling to DNA damage in eukaryotic cells.

Hallmarks of Splicing Defects in Cancer: Clinical Applications in the Era of Personalized Medicine

Alternative splicing promotes proteome diversity by using limited number of genes, a key control point of gene expression. Splicing is carried out by large macromolecular machineries, called spliceosome, composed of small RNAs and proteins. Alternative splicing is regulated by splicing regulatory cis-elements in RNA and trans-acting splicing factors that are often tightly regulated in a tissue-specific and developmental stage-specific manner. The biogenesis of ribonucleoprotein (RNP) complexes is strictly regulated to ensure that correct complements of RNA and proteins are coordinated in the right cell at the right time to support physiological functions. Any perturbations that impair formation of functional spliceosomes by disrupting the cis-elements, or by compromising RNA-binding or function of trans-factors can be deleterious to cells and result in pathological consequences. The recent discovery of oncogenic mutations in splicing factors, and growing evidence of the perturbed splicing in multiple types of cancer, underscores RNA processing defects as a critical driver of oncogenesis. These findings have resulted in a growing interest in targeting RNA splicing as a therapeutic approach for cancer treatment. This review summarizes our current understanding of splicing alterations in cancer, recent therapeutic efforts targeting splicing defects in cancer, and future potentials to develop novel cancer therapies.

SRPK1 acetylation modulates alternative splicing to regulate cisplatin resistance in breast cancer cells

Cisplatin and other platinum-based compounds are frequently used to treat breast cancer, but their utility is severely compromised by drug resistance. Many genes dictating drug responsiveness are subject to pre-mRNA alternative splicing which is regulated by key kinases such as the serine-arginine protein kinase 1 (SRPK1). However, its contribution to drug resistance remains controversial. In this study, we have identified that Tip60-mediated acetylation of SRPK1 is closely associated with chemotherapy sensitivity. In breast cancer cells, cisplatin induced SRPK1 acetylation but in the corresponding resistant cells, it reduced acetylation yet increased phosphorylation and kinase activity of SRPK1, favouring the splicing of some anti-apoptotic variants. Significantly, the cisplatin-resistant cells could be re-sensitized by enhancing SRPK1 acetylation or inhibiting its kinase activity. Hence, our study reveals a key role of SRPK1 in the development of cisplatin resistance in breast cancer cells and suggests a potential therapeutic avenue for overcoming chemotherapy resistance.

Wang et al. find that the therapeutic agent cisplatin has opposite effect on acetylation of serine-arginine protein kinase 1 (SRPK1) in cisplatin-resistant versus – sensitive breast cancer cells. Inhibiting SRPK1 activity or enhancing its acetylation re-sensitises cells to cisplatin, suggesting a potential strategy to treat cancers resistant to platinum-based therapy.

Serine-Arginine Protein Kinase 1 (SRPK1) as a Prognostic Factor and Potential Therapeutic Target in Cancer: Current Evidence and Future Perspectives

Cancer, a heterogeneous disease composed of tumor cells and microenvironment, is driven by deregulated processes such as increased proliferation, invasion, metastasis, angiogenesis, and evasion of apoptosis. Alternative splicing, a mechanism led by splicing factors, is implicated in carcinogenesis by affecting any of the processes above. Accumulating evidence suggests that serine-arginine protein kinase 1 (SRPK1), an enzyme that phosphorylates splicing factors rich in serine/arginine domains, has a prognostic and potential predictive role in various cancers. Its upregulation is correlated with higher tumor staging, grading, and shorter survival. SRPK1 is also highly expressed in the premalignant changes of some cancers, showing a potential role in the early steps of carcinogenesis. Of interest, its downregulation in preclinical models has mostly been tumor-suppressive and affected diverse processes heterogeneously, depending on the oncogenic context. In addition, targeting SRPK1 has enhanced sensitivity to platinum-based chemotherapy in some cancers. Lastly, its aberrant function has been noted not only in cancer cells but also in the endothelial cells of the microenvironment. Although the aforementioned evidence seems promising, more studies are needed to reinforce the use of SRPK1 inhibitors in clinical trials.

Long noncoding RNAs as biotargets in cisplatin-based drug resistance

Since its discovery, cisplatin has become the key drug in chemotherapy for cancers. Nevertheless, chemoresistance in cancers has become an impediment in using cisplatin for cancer treatment. The resistance toward cisplatin is multifaceted as it involves multiple cellular pathways. Ever since the knowledge of long noncoding RNAs as modulators of various molecular pathways came to light, the interest in the biological function of lncRNAs as biomarkers has increased dramatically. Numerous studies have reported the link between the dysregulation of lncRNAs and drug resistance in cancers. More importantly, several lncRNAs were found to be vital in regulating cisplatin resistance. Therefore, this review summarizes the recent efforts in linking between cisplatin resistance and different types of lncRNAs.

Chimeric antibody targeting SRPK-1 in the treatment of non-small cell lung cancer by inhibiting growth, migration and invasion

Non-small cell lung cancer (NSCLC) is one of the most common types of cancer in humans, and is characterized by rapid growth, migration, invasion and reoccurrence. Evidence has indicated that the protein and mRNA levels of serine‑arginine protein kinase‑1 (SRPK‑1) are upregulated in NSCLC tissues. However, the functions of SRPK1 and targeted therapy for SRPK1 in the progression and treatment of NSCLC remain to be fully elucidated. In the present study, the mRNA and protein expression levels of SRPK‑1 in NSCLC cells and tissues were analyzed using reverse transcription‑quantitative polymerase chain reaction analysis and SDS‑PAGE, and the role of SRPK1 in the progression of NSCLC was investigated. In addition, a chimeric antibody target for SRPK‑1 (ChanSRPK‑1) was constructed, and the therapeutic effects of ChanSRPK‑1 were investigated in H358‑bearing mice. The curative effects of ChanSRPK‑1 on the inhibition of growth, migration and invasion of NSCLC were also examined in vitro and in vivo. The results revealed that the mRNA and protein levels of SRPK‑1 were upregulated in NSCLC cells and tumor tissues. Higher expression of SRPK1 promoted NSCLC cell growth, migration and invasion, whereas lower expression of SRPK‑1 suppressed growth, migration and invasion of the NSCLC cells. Animal experiments demonstrated that ChanSRPK‑1 inhibited the β‑catenin/T‑cell factor complex. ChanSRPK‑1 treatment also downregulated the phosphorylation levels of glycogen synthase kinase 3-β and prolonged the survival of tumor‑bearing mice. Taken together, SRPK‑1 may offer potential as a therapeutic target oncogenic molecular in NSCLC, and ChanSRPK‑1 may be a therapeutic agent with functions as a target and for oncolytic therapy in the treatment of NSCLC.

Protein kinases that phosphorylate splicing factors: Roles in cancer development, progression and possible therapeutic options

Disturbed alternative splicing is a common feature of human tumors. Splicing factors that control alternative splicing are phosphorylated by multiple kinases, including these that specifically add phosphoryl groups to serine-arginine rich proteins (e.g. SR-protein kinases, cdc2-like kinases, topoisomerase 1), and protein kinases that govern key cellular signaling pathways (i.e. AKT). Phosphorylation of splicing factors regulates their subcellular localization and interactions with target transcripts and protein partners, and thus significantly contributes the final result of splicing reactions. In this review we aim to summarize the current knowledge on the role of splicing kinases in cancer. Published studies and recently released data of The Cancer Genome Atlas demonstrate that expressions and activities of splicing kinases are commonly disturbed in cancers. Aberrant functioning of splicing kinases results in changed alternative splicing of tumor suppressors (e.g. p53) and regulators of cell signaling (e.g. MAPKs), apoptosis (e.g. MCL), and angiogenesis (VEGF). Splicing kinases act in complicated regulatory networks in which they mutually affect each other's activity to provide tight control of cellular signaling. Dysregulation of these regulatory networks contributes to oncogenic transformation, uncontrolled proliferation, enhanced migration and invasion. Furthermore, the activities of splicing kinases significantly contribute to cellular responses to genotoxic stress. In conclusion, published data provide strong evidence that splicing kinases emerge as important regulators of key processes governing malignant transformation, progression, and response to therapeutic treatments, suggesting their potential as clinically relevant targets.

Splicing-factor alterations in cancers

Tumor-associated alterations in RNA splicing result either from mutations in splicing-regulatory elements or changes in components of the splicing machinery. This review summarizes our current understanding of the role of splicing-factor alterations in human cancers. We describe splicing-factor alterations detected in human tumors and the resulting changes in splicing, highlighting cell-type-specific similarities and differences. We review the mechanisms of splicing-factor regulation in normal and cancer cells. Finally, we summarize recent efforts to develop novel cancer therapies, based on targeting either the oncogenic splicing events or their upstream splicing regulators.

Expression of SRPK1 in gliomas and its role in glioma cell lines viability

Among factors regulating the splicing of major importance is serine/arginine protein kinase 1 (SRPK1) that phosphorylates SR splicing factors. SRPK1 is expressed in the mammalian central nervous system in a region- and neuron-specific manner. Based on previous observations that glial cells are practically devoid of SRPK1 and reports showing aberrant expression of SRPK1 in numerous tumors, but with conflicting roles, this study aims to investigate the expression of SRPK1 in glioma and its influence on tumor cell biological features. As shown by immunohistochemical analysis, malignant glioma cells express SRPK1 in glioblastomas with significant association between SRPK1 expression and patients' survival. SRPK1 expression was also significantly upregulated at the messenger RNA (mRNA) and protein level in glioma cell lines. Small interfering RNA-mediated downregulation of SRPK1 had little effect on cell viability, while it slightly enhanced the sensitivity of cells to killing by cisplatin. These results support the idea that at least in vitro, the effect of SRPK1 knockdown on the viability of glioma cell lines is rather limited, while the in vivo effects could be attributed to the modulation of angiogenesis by SRPK1.

The influence of SRPK1 on glioma apoptosis, metastasis, and angiogenesis through the PI3K/Akt signaling pathway under normoxia

Gliomas, the most common primary brain tumors, have low survival rates and poorly defined molecular mechanisms to target for treatment. Serine/arginine SR protein kinases 1 (SRPK1) can highly and specifically phosphorylate the SR protein found in many tumors, which can influence cell proliferation and angiogenesis. However, the roles and regulatory mechanisms of SRPK1 in gliomas are not understood. The aim of this study was to determine the functions and regulation of SRPK1 in gliomas. We found that SRPK1 inhibition induces early apoptosis and significantly inhibits xenograft tumor growth. Our results indicate that SRPK1 affects Akt and eIF4E phosphorylation, Bax and Bcl-2 activation, and HIF-1 and VEGF production in glioma cells. Moreover, transfection of SRPK1 siRNA strongly reduced cell invasion and migration by regulating the expression of MMP2 and MMP9 and significantly decreased the volume of tumors and angiogenesis. We show here that a strong link exists among SRPK1, Akt, eIF4E, HIF-1, and VEGF activity that is functionally involved in apoptosis, metastasis, and angiogenesis of gliomas under normoxic conditions. Thus, SRPK1 may be a potential anticancer target to inhibit glioma progression.

Elevated SRPK1 lessens apoptosis in breast cancer cells through RBM4-regulated splicing events

Imbalanced splicing of premessenger RNA is typical of tumorous malignancies, and the regulatory mechanisms involved in several tumorigenesis-associated splicing events are identified. Elevated expression of serine-arginine protein kinase 1 (SRPK1) may participate in the pathway responsible for the dysregulation of splicing events in malignant tumor cells. In this study, we observed a correlation between the cytoplasmic accumulation of RNA-binding motif protein 4 (RBM4) and up-regulated SRPK1 in breast cancer cells. The production of the IR-B and MCL-1S transcripts was induced separately by the overexpression of RBM4 and SRPK1 gene silencing. Overexpressed RBM4 simultaneously bound to the CU-rich elements within the MCL-1 exon2 and the downstream intron, which subsequently facilitated the exclusion of the regulated exon. Breast cancer cells are deprived of apoptotic resistance through the RBM4-mediated up-regulation of the IR-B and MCL-1S transcripts. These findings suggest that the splicing events regulated by the SRPK1-RMB4 network may contribute to tumorigenesis through altered sensitivity to apoptotic signals in breast cancer cells.

Serine-arginine protein kinase 1 is associated with breast cancer progression and poor patient survival

Breast cancer is the most common cancer and the second leading cause of mortality for women worldwide. It is necessary to identify valuable molecular markers to predict breast cancer progression in patients and treatment effect. Serine-arginine protein kinase 1 (SRPK1), a member of SR kinase family, phosphorylates the SR splicing factors which plays essential roles in normal cell development and multiple human diseases. In the current study, we wanted to explore if there are any relationships between SRPK1 expression in breast cancer and its clinical characteristics. The results showed that SRPK1 is upregulated in breast cancer cell lines and tissues at both mRNA and protein levels, measured by quantitative reverse transcriptase PCR and Western blotting. Immunohistochemical analysis showed a high expression of SRPK1 in 132 paraffin samples of patients with breast cancer; statistical analyses demonstrated that high expression of SRPK1 significantly correlated with clinical staging of patients with breast cancer (P < 0.001), TNM classification (P < 0.05). Low expression of SRPK1 leads to longer survival time, while high expression of SRPK1 leads to shorter survival time of patients. Multivariate analysis revealed that upregulation of SRPK1 might be an independent prognostic marker for the outcomes of patients with breast cancer. In conclusion, upregulation of SRPK1 might play an important role in the progression of breast cancer and might be considered as the potential diagnostic and therapeutic target to this malignancy.

Both decreased and increased SRPK1 levels promote cancer by interfering with PHLPP-mediated dephosphorylation of Akt

Akt activation is a hallmark of human cancers. Here, we report a critical mechanism for regulation of Akt activity by the splicing kinase SRPK1, a downstream Akt target for transducing growth signals to regulate splicing. Surprisingly, we find that SRPK1 has a tumor suppressor function because ablation of SRPK1 in mouse embryonic fibroblasts induces cell transformation. We link the phenotype to constitutive Akt activation from genome-wide phosphoproteomics analysis and discover that downregulated SRPK1 impairs the recruitment of the Akt phosphatase PHLPP1 (pleckstrin homology (PH) domain leucine-rich repeat protein phosphatase) to Akt. Interestingly, SRPK1 overexpression is also tumorigenic because excess SRPK1 squelches PHLPP1. Thus, aberrant SRPK1 expression in either direction induces constitutive Akt activation, providing a mechanistic basis for previous observations that SRPK1 is downregulated in some cancer contexts and upregulated in others.

SRPK1 Dissimilarly Impacts on the Growth, Metastasis, Chemosensitivity and Angiogenesis of Glioma in Normoxic and Hypoxic Conditions

Glioma is among the ten most common causes of cancer-related death and has no effective treatment for it, so we are trying to find a new target for anticancer treatment. This study investigates the different expression of SRPK1 as a novel protein in glioma, which can influence tumor cells biological characteristics in normoxic and hypoxic environment. The expression levels of SRPK1 protein in glioma cell lines transfected with siSRPK1 or not were examined using immunofluorescence, RT-PCR and Western blot analysis, respectively. The impact of SRPK1 on the biological characteristics of U251 cells was further studied using methylthiazol tetrazolium assays, flow cytometry, and Transwell invasion chamber assays. The results showed that knockdown of SRPK1 inhibited tumor cells growth, invasion and migration in normoxic condition, but portion of the effect could be reversed in hypoxia. SRPK1 expression was induced in glioma cells by DDP treated, but not TMZ, in both normoxia and hypoxia conditions. We propose SRPK1 as a new molecular player contributing to the early treatment of glioma.

Molecular Insights on Post-chemotherapy Retinoblastoma by Microarray Gene Expression Analysis

PURPOSE

Management of Retinoblastoma (RB), a pediatric ocular cancer is limited by drug-resistance and drug-dosage related side effects during chemotherapy. Molecular de-regulation in post-chemotherapy RB tumors was investigated.

MATERIALS AND METHODS

cDNA microarray analysis of two post-chemotherapy and one pre-chemotherapy RB tumor tissues was performed, followed by Principle Component Analysis, Gene ontology, Pathway Enrichment analysis and Biological Analysis Network (BAN) modeling. The drug modulation role of two significantly up-regulated genes (p≤0.05) - Ect2 (Epithelial-cell-transforming-sequence-2), and PRAME (preferentially-expressed-Antigen-in-Melanoma) was assessed by qRT-PCR, immunohistochemistry and cell viability assays.

RESULTS

Differential up-regulation of 1672 genes and down-regulation of 2538 genes was observed in RB tissues (relative to normal adult retina), while 1419 genes were commonly de-regulated between pre-chemotherapy and post- chemotherapy RB. Twenty one key gene ontology categories, pathways, biomarkers and phenotype groups harboring 250 differentially expressed genes were dys-regulated (EZH2, NCoR1, MYBL2, RB1, STAMN1, SYK, JAK1/2, STAT1/2, PLK2/4, BIRC5, LAMN1, Ect2, PRAME and ABCC4). Differential molecular expressions of PRAME and Ect2 in RB tumors with and without chemotherapy were analyzed. There was neither up- regulation of MRP1, nor any significant shift in chemotherapeutic IC50, in PRAME over-expressed versus non-transfected RB cells.

CONCLUSION

Cell cycle regulatory genes were dys-regulated post-chemotherapy. Ect2 gene was expressed in response to chemotherapy-induced stress. PRAME does not contribute to drug resistance in RB, yet its nuclear localization and BAN information, points to its possible regulatory role in RB.

SRPK1 contributes to malignancy of hepatocellular carcinoma through a possible mechanism involving PI3K/Akt

Protein kinases are important regulators in biologic processes. Aberrant expression of protein kinases often causes diseases including cancer. In the present study, we found that the serine-arginine protein kinase 1 (SRPK1) might be involved in hepatocellular carcinoma (HCC) proliferation from a kinome screen using a loss-of-function approach. In clinical samples, SRPK1 was frequently up-regulated in HCCs as compared with adjacent non-tumor tissues at both mRNA and protein levels. Functional studies indicated that overexpression of wild-type SRPK1 promoted HCC cell proliferation, while forced expression of the kinase-dead mutant of SRPK1 or RNA interference against SRPK1 suppressed cell growth and malignancy as measured in soft agar assay. The kinase-dead mutant of SRPK1 also inhibited subcutaneous xenografts' growth of HCC cells in nude mice. Furthermore, western bolt analysis showed overexpression of wild-type SRPK1 enhanced Akt phosphorylation and knockdown of SRPK1 by RNA interference attenuated Akt phosphorylation induced by epidermal growth factor. Meanwhile, overexpression of wild-type SRPK1 also induced a concurrent increase in the total tyrosine phosphorylation of phosphotidylinositol-3 kinase p110α subunit, indicating a functional link between SRPK1 and PI3K/Akt signaling. Our findings suggest that SRPK1 plays an oncogenic role and could be a potential therapeutic target in HCC.

Regulation of splicing by SR proteins and SR protein-specific kinases

Genomic sequencing reveals similar but limited numbers of protein-coding genes in different genomes, which begs the question of how organismal diversities are generated. Alternative pre-mRNA splicing, a widespread phenomenon in higher eukaryotic genomes, is thought to provide a mechanism to increase the complexity of the proteome and introduce additional layers for regulating gene expression in different cell types and during development. Among a large number of factors implicated in the splicing regulation are the SR protein family of splicing factors and SR protein-specific kinases. Here, we summarize the rules for SR proteins to function as splicing regulators, which depend on where they bind in exons versus intronic regions, on alternative exons versus flanking competing exons, and on cooperative as well as competitive binding between different SR protein family members on many of those locations. We review the importance of cycles of SR protein phosphorylation/dephosphorylation in the splicing reaction with emphasis on the recent molecular insight into the role of SR protein phosphorylation in early steps of spliceosome assembly. Finally, we highlight recent discoveries of SR protein-specific kinases in transducing growth signals to regulate alternative splicing in the nucleus and the connection of both SR proteins and SR protein kinases to human diseases, particularly cancer.

A clinical update and radiologic review of pediatric orbital and ocular tumors

While pediatric orbital tumors are most often managed in tertiary care centers, clinicians should be aware of the signs of intraocular and orbital neoplasms. In the pediatric population, a delay in diagnosis of orbital and intraocular lesions, even if benign, can lead to vision loss and deformity. Intraocular lesions reviewed are retinoblastoma, medulloepithelioma, and retinal astrocytic hamartoma. Orbital neoplasms reviewed are rhabdomyosarcoma, neuroblastoma metastases, optic pathway glioma, plexiform neurofibroma, leukemia, lymphoprolipherative disease, orbital inflammatory syndrome, dermoid and epidermoid inclusion cysts, and Langerhans' cell histiocytosis. Vascular lesions reviewed are infantile hemangioma and venous lymphatic malformation. In conjunction with clinical examination, high-resolution ophthalmic imaging and radiologic imaging play an important role in making a diagnosis and differentiating between benign and likely malignant processes. The radiologic imaging characteristics of these lesions will be discussed to facilitate prompt diagnosis and treatment. The current treatment modalities and management of tumors will also be reviewed.

Identification and Insilico Analysis of Retinoblastoma Serum microRNA Profile and Gene Targets Towards Prediction of Novel Serum Biomarkers

Retinoblastoma (RB) is a malignant tumor of the retina seen in children, and potential non invasive biomarkers are in need for rapid diagnosis and for prognosticating the therapy. This study was undertaken to identify the differentially expressed miRNAs in the serum of children with RB in comparison with the normal age matched serum, to analyze its concurrence with the existing RB tumor miRNA profile, to identify its novel gene targets specific to RB, and to study the expression of a few of the identified oncogenic miRNAs in the advanced stage primary RB patient’s serum sample. MiRNA profiling was performed on 14 pooled serum from children with advanced RB and 14 normal age matched serum samples, wherein 21 miRNAs were found to be upregulated (fold change ≤ −2.0, P ≤ 0.05) and 24 to be downregulated (fold change ≥ +2.0, P ≤ 0.05). Furthermore, intersection of 59 significantly deregulated miRNAs identified from RB tumor profiles with that of miRNAs detected in serum profile revealed that 33 miRNAs had followed a similar deregulation pattern in RB serum. Later we validated a few of the miRNAs (miRNA 17-92) identified by microarray in the RB patient serum samples (n = 20) by using qRT-PCR. Expression of the oncogenic miRNAs, miR-17, miR-18a, and miR-20a by qRT-PCR was significant in the serum samples exploring the potential of serum miRNAs identification as noninvasive diagnosis. Moreover, from miRNA gene target prediction, key regulatory genes of cell proliferation, apoptosis, and positive and negative regulatory networks involved in RB progression were identified in the gene expression profile of RB tumors. Therefore, these identified miRNAs and their corresponding target genes could give insights on potential biomarkers and key events involved in the RB pathway.

Elevated expression of the serine-arginine protein kinase 1 gene in ovarian cancer and its role in Cisplatin cytotoxicity in vitro

Alternatively spliced variants of several oncogenes and tumor suppressors have been shown to be important for their tumorigenicity. In the present study we have tested whether serine-arginine protein kinase 1 (SRPK1), a major regulator of splicing factors, is involved in ovarian cancer progression and plays a role in chemo-sensitivity. By Western blot analyses, SRPK1 protein was found to be overexpressed in 4 out of 6 ovarian cancer cell lines as compared with an immortalized ovarian surface epithelial cell line; and in 55% of ovarian tumor samples as compared with non-neoplastic ovarian tissue samples. Reduction of SRPK1 expression using small interfering RNA (siRNA) encoding small hairpin RNA in ovarian cancer cells led to (i) reduced cell proliferation rate, slower cell cycle progression and compromised anchorage-independent growth and migration ability in vitro, (ii) decreased level of phosphorylation of multiple serine-arginine proteins, and P44/42MAPK and AKT proteins, and (iii) enhanced sensitivity to cisplatin. Together, these results suggest that elevated SRPK1 expression may play a role in ovarian tumorigenesis and SRPK1 may be a potential target for ovarian cancer therapy.

MicroRNA-9 inhibition of cell proliferation and identification of novel miR-9 targets by transcriptome profiling in breast cancer cells

Although underexpression of miR-9 in cancer cells is reported in many cancer types, it is currently difficult to classify miR-9 as a tumor suppressor or an oncomir. We demonstrate that miR-9 expression is down-regulated in MCF-7 and MDA-MB-231 breast cancer cells compared with MCF-10-2A normal breast cell line. Increasing miR-9 expression levels in breast cancer cells induced anti-proliferative, anti-invasive, and pro-apoptotic activity. In addition, microarray profiling of the transcriptome of MCF-7 cells overexpressing miR-9 identified six novel direct miR-9 targets (AP3B1, CCNG1, LARP1, MTHFD1L, MTHFD2, and SRPK1). Among these, MTHFD2 was identified as a miR-9 target gene that affects cell proliferation. Knockdown of MTHFD2 mimicked the effect observed when miR-9 was overexpressed by decreasing cell viability and increasing apoptotic activity. Despite variable effects on different cell lines, proliferative and anti-apoptotic activity of MTHFD2 was demonstrated whereby it could escape from miR-9-directed suppression (by overexpression of MTHFD2 with mutated miR-9 binding sites). Furthermore, endogenous expression levels of miR-9 and MTHFD2 displayed inverse expression profiles in primary breast tumor samples compared with normal breast samples; miR-9 was down-regulated, and MTHFD2 was up-regulated. These results indicate anti-proliferative and pro-apoptotic activity of miR-9 and that direct targeting of MTHFD2 can contribute to tumor suppressor-like activity of miR-9 in breast cancer cells.

The Akt-SRPK-SR axis constitutes a major pathway in transducing EGF signaling to regulate alternative splicing in the nucleus

Pre-mRNA splicing is regulated by developmental and environmental cues, but little is known about how specific signals are transduced in mammalian cells to regulate this critical gene expression step. Here, we report massive reprogramming of alternative splicing in response to EGF signaling. By blocking individual branches in EGF signaling, we found that Akt activation plays a major role, while other branches, such as the JAK/STAT and ERK pathways, make minor contributions to EGF-induced splicing. Activated Akt next branches to SR protein-specific kinases, rather than mTOR, by inducing SRPK autophosphorylation that switches the splicing kinases from Hsp70- to Hsp90-containing complexes. This leads to enhanced SRPK nuclear translocation and SR protein phosphorylation. These findings reveal a major signal transduction pathway for regulated splicing and place SRPKs in a central position in the pathway, consistent with their reputed roles in a large number of human cancers.

WT1 mutants reveal SRPK1 to be a downstream angiogenesis target by altering VEGF splicing

Angiogenesis is regulated by the balance of proangiogenic VEGF(165) and antiangiogenic VEGF(165)b splice isoforms. Mutations in WT1, the Wilms' tumor suppressor gene, suppress VEGF(165)b and cause abnormal gonadogenesis, renal failure, and Wilms' tumors. In WT1 mutant cells, reduced VEGF(165)b was due to lack of WT1-mediated transcriptional repression of the splicing-factor kinase SRPK1. WT1 bound to the SRPK1 promoter, and repressed expression through a specific WT1 binding site. In WT1 mutant cells SRPK1-mediated hyperphosphorylation of the oncogenic RNA binding protein SRSF1 regulated splicing of VEGF and rendered WT1 mutant cells proangiogenic. Altered VEGF splicing was reversed by wild-type WT1, knockdown of SRSF1, or SRPK1 and inhibition of SRPK1, which prevented in vitro and in vivo angiogenesis and associated tumor growth.

Distribution of SRPK1 in human brain

Extensive alternative splicing is observed in the mammalian nervous system providing for protein diversity and specificity to accomplish the complex neuronal functions. Mechanisms underlying neuron specific splicing are not yet well understood. Among the factors regulating splicing of major importance are serine/arginine protein kinases (SRPKs) that phosphorylate SR splicing factors. SRPK1 is known to be expressed in the mammalian central nervous system. The present immunohistochemical study reveals a region- and neuron-specific localization of SRPK1 in human brain. The potential involvement of the kinase in the regulation of alternative splicing of various neuronal proteins is discussed.

Balance of pro- versus anti-angiogenic splice isoforms of vascular endothelial growth factor as a regulator of neuroblastoma growth

Neuroblastoma (NB) is the second most common extracranial tumour of childhood. Angiogenesis plays a crucial role in the growth and development of NB and vascular endothelial growth factor (VEGF), one of the most potent stimuli of angiogenesis, has been studied extensively in vitro. VEGF(165) has been shown to be the predominant angiogenic isoform expressed in NB cell lines and tumours. In this study, we investigated the anti-angiogenic isoform of VEGF-A, generated from distal splice site selection in the terminal exon of VEGF (VEGF(165)b) and shown to be down-regulated in epithelial malignancies. The expression of both the pro- (VEGF(xxx)) and the anti-angiogenic (VEGF(xxx)b) isoforms was compared in a range of NB and ganglioneuroma (GN) tumours. Whereas VEGF(xxx)b and VEGF(xxx) were both expressed in GN, specific up-regulation of the VEGF(xxx) isoforms was seen in NB at RNA and protein levels. Highly tumourigenic NB cell lines also showed up-regulation of the angiogenic isoforms relative to VEGF(xxx)b compared to less tumourigenic cell lines, and the isoforms were differentially secreted. These results indicate that VEGF(165) is up-regulated in NB and that there is a difference in the balance of isoform expression from anti-angiogenic VEGF(165)b to angiogenic VEGF(165). Treatment with recombinant human VEGF(165)b significantly reduced the growth rate of established xenografts of SK-N-BE(2)-C cells (4.24 +/- 1.01 fold increase in volume) compared with those treated with saline (9.76 +/- 3.58, p < 0.01). Microvascular density (MVD) was significantly decreased in rhVEGF(165)b-treated tumours (19.4 +/- 1.9 vessels/mm(3)) in contrast to the saline-treated tumours (45.5 +/- 8.6 vessels/mm(3)). VEGF(165)b had no significant effect on the proliferative or apoptotic activity, viability or cytotoxicity of SK-N-BE(2)-C cells after 48 h. In conclusion, VEGF(165)b is an effective inhibitor of NB growth. These findings provide the rationale for further investigation of VEGF(165)b in NB and other paediatric malignancies.