Downregulation of receptor for activated C-kinase 1 (RACK1) suppresses tumor growth by inhibiting tumor cell proliferation and tumor-associated angiogenesis

Ethanolic extract from Sophora moorcroftiana inhibit cell proliferation and alter the mechanical properties of human cervical cancer

BACKGROUND

Cervical cancer is one of the most common gynecological malignancies. Previous studies have shown that the ethanol extract of Sophora moorcroftiana seeds (EESMS) possesses an antiproliferative effect on several tumors in vitro. Therefore, in this study, we assessed the impact of EESMS on human cervical carcinoma (HeLa) cell proliferation.

METHODS

The proliferation and apoptotic effects of HeLa cells treated with EESMS were evaluated using 3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide assay, dual acridine orange/ethidium bromide double staining, flow cytometry, and western blotting. Single-cell level atomic force microscopy (AFM) was conducted to detect the mechanical properties of HeLa cells, and proteomics and bioinformatics methods were used to elucidate the molecular mechanisms of EESMS.

RESULTS

EESMS treatment inhibited HeLa cell proliferation by blocking the G0/G1 phase, increasing the expression of Caspase-3 and affecting its mechanical properties, and the EESMS indicated no significant inhibitory effect on mouse fibroblasts L929 cell line. In total, 218 differentially expressed proteins were identified using two-dimensional electrophoresis, and eight differentially expressed proteins were successfully identified using matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry. The differentially expressed proteins were involved in various cellular and biological processes.

CONCLUSION

This study provides a perspective on how cells change through biomechanics and a further theoretical foundation for the future application of Sophora moorcroftiana as a novel low-toxicity chemotherapy medication for treating human cervical cancer.

TRIM26 inhibited osteosarcoma progression through destabilizing RACK1 and thus inactivation of MEK/ERK signaling

Osteosarcoma is a highly aggressive malignant tumor that is common in the pediatric population and has a high rate of disability and mortality. Recent studies have suggested that the tripartite motif-containing family genes (TRIMs) play critical roles in oncogenesis in several cancers. TRIM26, one of the TRIMs family genes, was more frequently reported to exert a tumor-suppressive role, while its detailed functional roles in the osteosarcoma progression were still unknown and require further investigation. Herein, we found that TRIM26 was markedly downregulated in osteosarcoma tissues and cells. Survival analysis revealed that higher expression of TRIM26 was associated with better prognosis and its expression was an independent protective factor in osteosarcoma. Functional analysis demonstrated that overexpression of TRIM26 inhibited osteosarcoma cell proliferation and invasion via inhibiting the EMT process and MEK/ERK signaling. In contrast, the silence of TRIM26 caused the opposite effect. RACK1, a member of the Trp-Asp repeat protein family, was identified as a novel target of TRIM26. TRIM26 could interact with RACK1 and accelerate the degradation of RACK1, thus inactivation of MEK/ERK signaling. Overexpression of RACK1 could attenuate the inhibitory effect of TRIM26 overexpression on p-MEK1/2 and p-ERK1/2, and silence of RACK1 could partly impair the effect of TRIM26 knockdown-induced upregulation of p-MEK1/2 and p-ERK1/2. Further, a series of gain- and loss-of-function experiments showed that decreased malignant behaviors including cell proliferation and invasion in TRIM26-upregulated cells were reversed when RACK1 was overexpressed, whereas RACK1 knockdown diminished the increased malignant phenotypes in TRIM26-silenced osteosarcoma cells. In conclusion, our study indicated that TRIM26 inhibited osteosarcoma progression via promoting proteasomal degradation of RACK1, thereby resulting in inactivation of MEK/ERK signaling, and impeding the EMT process.

CircVPRBP inhibits nodal metastasis of cervical cancer by impeding RACK1 O-GlcNAcylation and stability

Lymph node (LN) metastasis is one of the most malignant clinical features in patients with cervical cancer (CCa). Understanding the mechanism of lymph node metastasis will provide treatment strategies for patients with CCa. Circular RNAs (circRNA) play a critical role in the development of human cancers. However, the role and mechanism of circRNAs in lymph node metastasis remain largely unknown. Here, it is reported that loss expression of circRNA circVPRBP was closely associated with LN metastasis and poor survival of CCa patients. In vitro and in vivo assays showed that circVPRBP overexpression notably inhibited lymphangiogenesis and LN metastasis, whereas RfxCas13d mediated silencing of circVPRBP promoted lymphangiogenesis and the ability of the cervical cancer cells to metastasize to the LNs. Mechanistically, circVPRBP could bind to RACK1 and shield the S122 O-GlcNAcylation site to promote RACK1 degradation, resulting in inhibition of Galectin-1 mediated lymphangiogenesis and LN metastasis in CCa. Taken together, the results demonstrate that circVPRBP is a potential prognostic biomarker and a novel therapeutic target for LN metastasis in CCa patients.

Hepatic RACK1 deletion disturbs lipid and glucose homeostasis independently of insulin resistance

Receptor for activated C kinase 1 (RACK1) is a versatile protein involved in multiple biological processes. In a previous study by Zhao et al., hepatic RACK1 deletion in mice led to an inhibition of autophagy, blocked autophagy-dependent lipolysis, and caused steatosis. Using the same mouse model (RACK1hep-/-), we revealed new roles of RACK1 in maintaining bile acid homeostasis and hepatic glucose uptake, which further affected circulatory lipid and glucose levels. To be specific, even under hepatic steatosis, the plasma lipids were generally reduced in RACK1hep-/- mouse, which was due to the suppression of intestinal lipid absorption. Accordingly, a decrease in total bile acid level was found in RACK1hep-/- livers, gallbladders, and small intestine tissues, and specific decrease of 12-hydroxylated bile acids was detected by liquid chromatography-mass spectrometry. Consistently, reduced expression of CYP8B1 was found. A decrease in hepatic glycogen storage was also observed, which might be due to the inhibited glucose uptake by GLUT2 insufficiency. Interestingly, RACK1-KO-inducing hepatic steatosis did not raise insulin resistance (IR) nor IR-inducing factors like endoplasmic reticulum stress and inflammation. In summary, this study uncovers that hepatic RACK1 might be required in maintaining bile acid homeostasis and glucose uptake in hepatocytes. This study also provides an additional case of hepatic steatosis disassociation with insulin resistance.

Quantitative proteomic profiling of tumor-associated vascular endothelial cells in colorectal cancer

To investigate the global proteomic profiles of vascular endothelial cells (VECs) in the tumor microenvironment and antiangiogenic therapy for colorectal cancer (CRC), matched pairs of normal (NVECs) and tumor-associated VECs (TVECs) were purified from CRC tissues by laser capture microdissection and subjected to iTRAQ-based quantitative proteomics analysis. Here, 216 differentially expressed proteins (DEPs) were identified and used for bioinformatics analysis. Interestingly, these proteins were implicated in epithelial mesenchymal transition (EMT), ECM-receptor interaction, focal adhesion, PI3K-Akt signaling pathway, angiogenesis and HIF-1 signaling pathway, which may play important roles in CRC angiogenesis. Among these DEPs we found that Tenascin-C (TNC) was upregulated in TVECs of CRC and correlated with CRC multistage carcinogenesis and metastasis. Furthermore, the reduction of tumor-derived TNC could attenuate human umbilical vein endothelial cell (HUVEC) proliferation, migration and tube formation through ITGB3/FAK/Akt signaling pathway. Based on the present work, we provided a large-scale proteomic profiling of VECs in CRC with quantitative information, a certain number of potential antiangiogenic targets and a novel vision in the angiogenesis bio-mechanism of CRC.

Summary: We provided large-scale proteomic profiling of vascular endothelial cells in colorectal cancer with quantitative information, a number of potential antiangiogenic targets and a novel vision in the angiogenesis bio-mechanism of CRC.

Downregulated expression of RACK1 results in pancreatic cancer growth and metastasis

Background

The expression and function of the Receptor for Activated C Kinase 1 (RACK1) in cancer growth and metastasis are confused in different cancers, especially in pancreatic ductal adenocarcinoma (PDAC).

Methods

One-hundred and eighty-two PDAC tissue specimens (95 males and 87 females) including pancreatic cancer tissue and para-carcinoma tissue were collected for analysis between 2005 to 2012. Blood phenotypic parameters using cell count and capillary electrophoresis were investigated. HE staining, real time PCR, Western blot analysis, and soft agar assays were performed to determine the role of RACK1.

Purpose

In this study, we aim to determine the specific role of RACK1 in the untility of PDAC.

Results

We found that RACK1 expression was significantly lower in pancreatic cancer tissue than in para-carcinoma normal pancreatic tissue both in clinic and mice with pancreatic cancer at the early stage. Our results suggested that RACK1 silence could significantly promote cell growth and metastasis of pancreatic cancer cells. But we found that the overexpression of RACK1 has the opposite effect in vitro. In vivo MIAPaca-2 cells overexpressing RACK1, the results demonstrated lower metastatic ability than MIAPaca-2 cells. RACK1 overexpression could decrease the NF-κB transactivation activity of MIAPaca-2 cells, which was consistent with the inhibitory effect of RACK1 overexpression on the pro-migration and pro-invasive target gene of NF-κB, while which could be increased by RACK1 silence. RACK1 silence also enhanced protein expression of pro-migration and pro-invasive NF-κB target genes, which on the contrary, could be reversed by IκBα. Besides, RACK1 expression was significantly associated with lymph node metastasis, vessels metastasis, invasion of nerves as well as TNM staging. The 3-year survival rate of patients with high RACK1 expression was significantly higher than those patients with low RACK1 expression. However, RACK1 expression was not an independent risk factor for of the long-term postoperative survival of patients with pancreatic cancer.

Conclusion

The obtained results in our study suggested that the low expression of RACK1 was associated with cancer cell growth and metastasis in pancreatic cancer through the activation of the NF-κB pathway. RACK1 could be a potential therapeutic drug target to pancreatic cancer and metastasis.

Molecular Features and mRNA Expression of the Receptor for Activated C Kinase 1 from Symbiodinium microadriaticum ssp. microadriaticum During Growth and the Light/Dark cycle

Two genes of the RACK1 homolog from the photosynthetic dinoflagellate Symbiodinium microadriaticum ssp. microadriaticum (SmicRACK1), termed SmicRACK1A and SmicRACK1B, were found tandemly arrayed and displayed a single synonymous substitution (T/C) encoding threonine. They included two exons of 942 bp each, encoding 313 amino acids with seven WD-40 repeats and two PKC-binding motifs. The protein theoretical mass and pI were 34,200 Da and 5.9, respectively. SmicRACK1 showed maximum identities with RACK1 homologs at the amino acid and nucleotide level, respectively, of 92 and 84% with S. minutum, and phylogenetic analysis revealed clustered related RACK1 sequences from the marine dinoflagellates S. minutum, Heterocapsa triquetra, Karenia brevis, and Alexandrium tamarense. Interestingly, light-dependent regulatory elements were found both within the 282 bp SmicRACK1A promotor sequence, and within an intergenic sequence of 359 nucleotides that separated both genes, which strongly suggest light-related functions. This was further supported by mRNA accumulation analysis, which fluctuated along the light and dark phases of the growth cycle showing maximum specific peaks under either condition. Finally, qRT-PCR analysis revealed differential SmicRACK1 mRNA accumulation with maxima at 6 and 20 d of culture. Our SmicRACK1 characterization suggests roles in active growth and proliferation, as well as light/dark cycle regulation in S. microadriaticum.

RACK1 Silencing Induces Cell Apoptosis and Inhibits Cell Proliferation in Hepatocellular Carcinoma MHCC97-H Cells

This study aimed to explore the effects of RACK1 gene silencing on the apoptosis and proliferation of hepatocellular carcinoma (HCC) MHCC97-H cells. After transfecting MHCC97-H cells with siRNA, RACK1 gene silencing model was established. The cells were divided into blank group, siRNA group and empty plasmid group, respectively. The mRNA and protein expressions of RACK1, cyclin D1 and BAX were determined by qRT-PCR and Western blotting. CCK-8 assay, flow cytometry and FITC-Annexin V/PI staining were used to determine cell viability, cell cycle and cell apoptosis, respectively. The results of qRT-PCR and Western blotting suggested that when compared with the blank group and the empty plasmid group, the mRNA and protein expressions of RACK1 and Cyclin D1 decreased significantly while the mRNA and protein BAX expressions increased substantially in the siRNA group (all P < 0.05). The results of CCK-8 assay revealed that the siRNA group exhibited significantly lower cell viability when compared with the blank group and the empty plasmid group (both P < 0.05); and the cell viability in the siRNA group decreased gradually with the increase of time. The results of flow cytometry and FITC-Annexin V/PI staining indicated that when compared with the blank group and the empty plasmid group, the proportion of cells in S phase was markedly lower and the apoptosis rate was significantly higher in the siRNA group (both P < 0.05). Our study suggests that inhibition of RACK1 could suppress cell proliferation and induce apoptosis in HCC MHCC97-H cells.

The interaction between RACK1 and WEE1 regulates the growth of gastric cancer cell line HGC27

Receptor of activated C Kinase 1 (RACK1) is an essential scaffold and anchoring protein, which serves an important role in multiple tumorigenesis signaling pathways. The present study aimed to investigate the expression of RACK1 in gastric cancer (GC), and its association with the occurrence and development of GC. In addition, the effect and mechanism of RACK1 overexpression on the growth, and proliferation of GC cells was examined. Firstly, the protein expression of RACK1 was detected in 70 cases of GC tissues and 30 cases of noncancerous tissues using immunohistochemical staining, and the association between clinical and pathological features of GC was analyzed. Secondly, the mRNA and protein expression of RACK1 was determined in the poorly-differentiated human gastric cancer cell line HGC27 and gastric epithelial cell line GES-1. The growth of HGC27 cells following the upregulation of RACK1 was detected using MTT method. Subsequently, the interaction and co-location between RACK1, and WEE1 homolog (S. pombe) (WEE1) in HGC27 cells was confirmed using co-immunoprecipitation and indirect immunofluorescence. The expression level of RACK1 in GC was significantly lower compared with that in pericarcinous tissues (P<0.05). The protein level of RACK1 expression correlated with tumor node metastasis stage, tumor differentiation and lymph node metastasis. The mRNA and protein levels of RACK1 in HGC27 cells were significantly reduced, and overexpressed RACK1 downregulated WEE1 protein expression, thus inhibiting the growth of HGC27 cells. Co-immunoprecipitation and immunofluorescence confirmed that RACK1, and WEE1 interacted and co-located in the cytoplasm of HGC27 cells. Therefore, the abnormal expression of RACK1 in GC tissues was identified to be involved in the occurrence and development of GC. Overexpression of RACK1 was able to inhibit the growth of HGC27 cells. The current study suggests that low expression of RACK1 is an important indicator of poor prognosis of GC. RACK1 and WEE1 interact to regulate the growth of HGC27 cells.

Inhibition of RACK1 ameliorates choroidal neovascularization formation in vitro and in vivo

Choroidal neovascularization (CNV) occurs as a result of age-related macular degeneration (AMD) and causes severe vision loss among elderly patients. The receptor for activated C-kinase 1 (RACK1) serves as a scaffold protein which is recently found to promote angiogenesis. However, the impact of RACK1 on the vascular endothelial growth factor (VEGF) expression in endothelial cells and subsequent choroidal angiogenesis formation remains to be elucidated. In this study, we found that RACK1 and VEGF expression increased, and reached the peak at 7d in mouse CNV model by laser application. Furthermore, on RPE/choroid cryosections, RACK1 co-localized with CD31, suggesting that RACK1 was expressed in endothelial cells. In vitro, RF/6A cell hypoxia model showed that RACK1 expression was up-regulated in parallel with hypoxia-induced factor 1 (HIF-1α) and VEGF expression, reaching the peak at 6h. Silencing of RACK1 suppressed the invasion and tube formation activity of RF/6A cells in ARPE-19 and RF/6A co-culture system, possibly through VEGF signal pathway. Overexpression of RACK1 showed the opposite effect. Intravitreal injection of anti-RACK1 monoclonal antibody predominantly decreased RACK1 and VEGF expression in mouse laser-induced CNV model. Meanwhile, anti-RACK1 monoclonal antibody intravitreal injection also decreased incidence of CNV and leakage area. These data indicated that RACK1 promoted CNV formation via VEGF pathway. Additionally, anti-RACK1 monoclonal antibody significantly decreased CNV in mouse model and may have therapeutic potential in human CNV.

Hypoxia-inducible factor-1 and associated upstream and downstream proteins in the pathophysiology and management of glioblastoma

Glioblastoma multiforme (GBM) is a highly aggressive brain tumor with an exceptionally poor patient outcome despite aggressive therapy including surgery, radiation, and chemotherapy. This aggressive phenotype may be associated with intratumoral hypoxia, which probably plays a key role in GBM tumor growth, development, and angiogenesis. A key regulator of cellular response to hypoxia is the protein hypoxia-inducible factor–1 (HIF-1). An examination of upstream hypoxic and nonhypoxic regulation of HIF-1 as well as a review of the downstream HIF-1– regulated proteins may provide further insight into the role of this transcription factor in GBM pathophysiology. Recent insights into upstream regulators that intimately interact with HIF-1 could provide potential therapeutic targets for treatment of this tumor. The same is potentially true for HIF-1–mediated pathways of glycolysis-, angiogenesis-, and invasion-promoting proteins. Thus, an understanding of the relationship between HIF-1, its upstream protein regulators, and its downstream transcribed genes in GBM pathogenesis could provide future treatment options for the care of patients with these tumors.

Impact of high dietary zinc on zinc accumulation, enzyme activity and proteomic profiles in the pancreas of piglets

The exocrine pancreas plays an important role in zinc homeostasis. Feeding very high (2000-3000mgzinc/kg diet) levels of zinc oxide to piglets for short periods is a common practice in the swine industry to improve performance and prevent diseases. The impact on pancreatic function and possible side effects during long-term feeding of high dietary zinc levels are still poorly understood. A total of 54 weaned piglets were either fed with low (57mg/kg, LZn), normal (164mg/kg, NZn) or high (2425mg/kg, HZn) zinc concentration in the diets. After 4 weeks of feeding, ten piglets per treatment were euthanized and pancreas samples were taken. Tissue zinc concentration and metallothionein abundance was greater with HZn compared with NZn and LZn (P<0.05). Similarly, activity of α-amylase, lipase, trypsin and chymotrypsin was higher with HZn as compared with NZn and LZn diets (P<0.05), whereas elastase activity was unchanged. Total trolox equivalent antioxidative capacity of pancreas tissue was higher with HZn diets compared with the other treatments (P<0.05). Pancreatic protein profiles of NZn and HZn fed piglets were obtained by 2D-DIGE technique and revealed 15 differentially expressed proteins out of 2100 detected spots (P<0.05). The differentially expressed proteins aldose reductase, eukaryotic elongation factor II and peroxiredoxin III were confirmed by immunoblotting. Identified proteins include zinc finger-containing transcription factors and proteins mainly associated with oxidative stress response and signal transduction in HZn compared with NZn pigs. Histologic examination however showed no morphologic changes. The results suggest that long-term supply of very high dietary zinc increases zinc and metallothionein concentration, and digestive enzyme activity, but also triggers oxidative stress reactions in the pancreas of young pigs. The data provide new insights into pancreatic function under outbalanced zinc homeostasis.

BMP4/Thrombospondin-1 loop paracrinically inhibits tumor angiogenesis and suppresses the growth of solid tumors

Bone morphogenetic protein 4 (BMP4) has potential as an anticancer agent. Recent studies have suggested that BMP4 inhibits the survival of cancer stem cells (CSCs) of neural and colon cancers. Here, we showed that BMP4 paracrinically inhibited tumor angiogenesis via the induction of Thrombospondin-1 (TSP1), and consequently suppressed tumor growth in vivo. Although HeLa (human cervical cancer), HCI-H460-LNM35 (highly metastatic human lung cancer) and B16 (murine melanoma) cells did not respond to the BMP4 treatment in vitro, the growth of xeno- and allografts of these cells was suppressed via reductions in tumor angiogenesis after intraperitoneal treatment with BMP4. When we assessed the mRNA expression of major angiogenesis-related factors in grafted tumors, we found that the expression of TSP1 was significantly upregulated by BMP4 administration. We then confirmed that BMP4 was less effective in suppressing the tumor growth of TSP1-knockdown cancer cells. Furthermore, we found that BMP4 reduced vascular endothelial growth factor (VEGF) expression in vivo in a TSP1-dependent manner, which indicates that BMP4 interfered with the stabilization of tumor angiogenesis. In conclusion, the BMP4/TSP1 loop paracrinically suppressed tumor angiogenesis in the tumor microenvironment, which subsequently reduced the growth of tumors. BMP4 may become an antitumor agent and open a new field of antiangiogenic therapy.

RACK1 promotes prostate cancer cell proliferation, invasion and metastasis

The aim of the present study was to investigate the functions of RACK1 and its involvement in mechanisms of prostate cancer (PC) cell proliferation, invasion and metastasis. The proliferation, invasion and metastasis of stably transfected DU145 cells with RACK1 was evaluated in vitro as well as in vivo following the establishment of nude mouse models. The expression of Ki67, RACK1, PTEN and androgen receptor (AR) in PC was detected by immunohistochemical analysis. Our results indicated that RACK1 promotes PC cell proliferation, invasion and metastasis in vitro and in vivo. However, knockdown of RACK1 by siRNA in vitro inhibited PC cell proliferation, migration and invasion. PTEN downregulation and Ki67 upregulation were also altered with the upregulation of RACK1; RACK1 staining was strongly correlated with PTEN downregulation and Ki67 upregulation. These data demonstrated that increased RACK1 expression is important in promoting PC cell proliferation, invasion and metastasis in vitro and in vivo.

Lyn, a Src family kinase, regulates activation of epidermal growth factor receptors in lung adenocarcinoma cells

BACKGROUND

Activation of receptors for growth factors on lung epithelial cells is essential for transformation into tumor cells, supporting their viability and proliferation. In most lung cancer patients, EGFR is constitutively activated without evidence of mutation. Defining mechanisms for constitutive activation of EGFR could elucidate additional targets for therapy of lung cancers.

METHODS

The approach was to identify lung cancer cell lines with constitutively activated EGFR and use systematic selection of inhibitors to evaluate their effects on specific EGFR phosphorylations and downstream signaling pathways. Interactions between receptors, kinases, and scaffolding proteins were investigated by co-immunoprecipitation plus Western blotting.

RESULTS

The results revealed a dependence on Src family of tyrosine kinases for downstream signaling and cell growth. Lyn, a Src family kinase functional in normal and malignant B-lymphocytes, was a defining signal transducer required for EGFR signaling in Calu3 cell line. Src family kinase activation in turn, was dependent on PKCßII. Lyn and PKC exist in membrane complexes of RACK1 and in association with EGFR which pairs with other receptor partners. Silencing of Lyn expression with interfering siRNA decreased EGFR activation and cell viability.

CONCLUSIONS

The importance of Src family kinases and PKCßII in the initiation of the EGFR signaling pathway in lung tumor cells was demonstrated. We conclude that phosphorylation of EGFR is mediated through PKCßII regulation of Lyn activation, and occurs in association with RACK1 and Cbp/PAG proteins. We suggest that protein complexes in cell membranes, including lipid rafts, may serve as novel targets for combination therapies with EGFR and Src Family Kinase inhibitors in lung cancer.

Mutation spectrum in human colorectal cancers and potential functional relevance

Background

Somatic variants, which occur in the genome of all cells, are well accepted to play a critical role in cancer development, as their accumulation in genes could affect cell proliferations and cell cycle.

Methods

In order to understand the role of somatic mutations in human colorectal cancers, we characterized the mutation spectrum in two colorectal tumor tissues and their matched normal tissues, by analyzing deep-sequenced transcriptome data.

Results

We found a higher mutation rate of somatic variants in tumor tissues in comparison with normal tissues, but no trend was observed for mutation properties. By applying a series of stringent filters, we identified 418 genes with tumor specific disruptive somatic variants. Of these genes, three genes in mucin protein family (MUC2, MUC4, and MU12) are of particular interests. It has been reported that the expression of mucin proteins was correlated with the progression of colorectal cancer therefore somatic variants within those genes can interrupt their normal expression and thus contribute to the tumorigenesis.

Conclusions

Our findings provide evidence of the utility of RNA-Seq in mutation screening in cancer studies, and suggest a list of candidate genes for future colorectal cancer diagnosis and treatment.

A comparative transcriptomic analysis reveals conserved features of stem cell pluripotency in planarians and mammals

Many long-lived species of animals require the function of adult stem cells throughout their lives. However, the transcriptomes of stem cells in invertebrates and vertebrates have not been compared, and consequently, ancestral regulatory circuits that control stem cell populations remain poorly defined. In this study, we have used data from high-throughput RNA sequencing to compare the transcriptomes of pluripotent adult stem cells from planarians with the transcriptomes of human and mouse pluripotent embryonic stem cells. From a stringently defined set of 4,432 orthologs shared between planarians, mice and humans, we identified 123 conserved genes that are ≥5-fold differentially expressed in stem cells from all three species. Guided by this gene set, we used RNAi screening in adult planarians to discover novel stem cell regulators, which we found to affect the stem cell-associated functions of tissue homeostasis, regeneration, and stem cell maintenance. Examples of genes that disrupted these processes included the orthologs of TBL3, PSD12, TTC27, and RACK1. From these analyses, we concluded that by comparing stem cell transcriptomes from diverse species, it is possible to uncover conserved factors that function in stem cell biology. These results provide insights into which genes comprised the ancestral circuitry underlying the control of stem cell self-renewal and pluripotency.

Loss of the starvation-induced gene Rack1 leads to glycogen deficiency and impaired autophagic responses in Drosophila

Autophagy delivers cytoplasmic material for lysosomal degradation in eukaryotic cells. Starvation induces high levels of autophagy to promote survival in the lack of nutrients. We compared genome-wide transcriptional profiles of fed and starved control, autophagy-deficient Atg7 and Atg1 null mutant Drosophila larvae to search for novel regulators of autophagy. Genes involved in catabolic processes including autophagy were transcriptionally upregulated in all cases. We also detected repression of genes involved in DNA replication in autophagy mutants compared with control animals. The expression of Rack1 (receptor of activated protein kinase C 1) increased 4.1- to 5.5-fold during nutrient deprivation in all three genotypes. The scaffold protein Rack1 plays a role in a wide range of processes including translation, cell adhesion and migration, cell survival and cancer. Loss of Rack1 led to attenuated autophagic response to starvation, and glycogen stores were decreased 11.8-fold in Rack1 mutant cells. Endogenous Rack1 partially colocalized with GFP-Atg8a and early autophagic structures on the ultrastructural level, suggesting its involvement in autophagosome formation. Endogenous Rack1 also showed a high degree of colocalization with glycogen particles in the larval fat body, and with Shaggy, the Drosophila homolog of glycogen synthase kinase 3B (GSK-3B). Our results, for the first time, demonstrated the fundamental role of Rack1 in autophagy and glycogen synthesis.

Receptor for activated C kinase 1 (RACK1): a regulator for migration and invasion in oral squamous cell carcinoma cells

PURPOSE

Receptor of activated protein kinase C 1 (RACK1) has been identified as an anchoring or adaptor protein in multiple intracellular signal transduction pathways. Our previous study has showed that the expression of RACK1 was paralleled with proliferation and correlated with metastasis and clinical outcome. However, the underlined mechanism has not been uncovered.

MATERIALS AND METHODS

We first selected a most effective siRNA among three siRNAs (siRNA-1, siRNA-2 and siRNA-3) targeting different regions in the RACK1 mRNA and re-evaluated the anticancer effect of RACK1 silencing on HSC-3 and Cal-27 cell lines by cell growth inhibition. And then, we investigated whether knockdown of RACK1 could inhibit cell adhesion, migration and invasion in these two cell lines. To further understand the molecular mechanism of RACK1 in these processes, the expressions of EGFR, pEGFR, HER2, MMP-2 and MMP-9 were detected by western blot.

RESULTS

We verified that the silence of RACK1 gene in two OSCC cell lines could not only inhibit cell proliferation but also decrease the invasion, migration and adhesion capability of the tumor cells. Further, western blot analysis deduced that it might be related to the decrease in protein expression of EGFR, pEGFR, HER2, MMP-2 and MMP-9.

CONCLUSION

Our results clearly showed the significance of RACK1-induced OSCC cell migration, invasion and adhesion, which could explain the underlined mechanism of the effect of the gene on metastasis and clinical outcome. Also, our results confirmed its role to be a prognostic indicator and a promising drug target for OSCC cell metastasis.