Secreted protein acidic, rich in cysteine induces pulp cell migration via alphavbeta3 integrin and extracellular signal-regulated kinase

SPARC promotes leukemic cell growth and predicts acute myeloid leukemia outcome

Aberrant expression of the secreted protein, acidic, cysteine-rich (osteonectin) (SPARC) gene, which encodes a matricellular protein that participates in normal tissue remodeling, is associated with a variety of diseases including cancer, but the contribution of SPARC to malignant growth remains controversial. We previously reported that SPARC was among the most upregulated genes in cytogenetically normal acute myeloid leukemia (CN-AML) patients with gene-expression profiles predictive of unfavorable outcome, such as mutations in isocitrate dehydrogenase 2 (IDH2-R172) and overexpression of the oncogenes brain and acute leukemia, cytoplasmic (BAALC) and v-ets erythroblastosis virus E26 oncogene homolog (ERG). In contrast, SPARC was downregulated in CN-AML patients harboring mutations in nucleophosmin (NPM1) that are associated with favorable prognosis. Based on these observations, we hypothesized that SPARC expression is clinically relevant in AML. Here, we found that SPARC overexpression is associated with adverse outcome in CN-AML patients and promotes aggressive leukemia growth in murine models of AML. In leukemia cells, SPARC expression was mediated by the SP1/NF-κB transactivation complex. Furthermore, secreted SPARC activated the integrin-linked kinase/AKT (ILK/AKT) pathway, likely via integrin interaction, and subsequent β-catenin signaling, which is involved in leukemia cell self-renewal. Pharmacologic inhibition of the SP1/NF-κB complex resulted in SPARC downregulation and leukemia growth inhibition. Together, our data indicate that evaluation of SPARC expression has prognosticative value and SPARC is a potential therapeutic target for AML.

Matrikine and matricellular regulators of EGF receptor signaling on cancer cell migration and invasion

Cancer invasion is a complex process requiring, among other events, extensive remodeling of the extracellular matrix including deposition of pro-migratory and pro-proliferative moieties. In recent years, it has been described that while invading through matrices cancer cells can change shape and adapt their migration strategies depending on the microenvironmental context. Although intracellular signaling pathways governing the mesenchymal to amoeboid migration shift and vice versa have been mostly elucidated, the extracellular signals promoting these shifts are largely unknown. In this review, we summarize findings that point to matrikines that bind specifically to the EGF receptor as matricellular molecules that enable cancer cell migrational plasticity and promote invasion.

Integrated analysis of global mRNA and protein expression data in HEK293 cells overexpressing PRL-1

BACKGROUND

The protein tyrosine phosphatase PRL-1 represents a putative oncogene with wide-ranging cellular effects. Overexpression of PRL-1 can promote cell proliferation, survival, migration, invasion, and metastasis, but the underlying mechanisms by which it influences these processes remain poorly understood.

METHODOLOGY

To increase our comprehension of PRL-1 mediated signaling events, we employed transcriptional profiling (DNA microarray) and proteomics (mass spectrometry) to perform a thorough characterization of the global molecular changes in gene expression that occur in response to stable PRL-1 overexpression in a relevant model system (HEK293).

PRINCIPAL FINDINGS

Overexpression of PRL-1 led to several significant changes in the mRNA and protein expression profiles of HEK293 cells. The differentially expressed gene set was highly enriched in genes involved in cytoskeletal remodeling, integrin-mediated cell-matrix adhesion, and RNA recognition and splicing. In particular, members of the Rho signaling pathway and molecules that converge on this pathway were heavily influenced by PRL-1 overexpression, supporting observations from previous studies that link PRL-1 to the Rho GTPase signaling network. In addition, several genes not previously associated with PRL-1 were found to be significantly altered by its expression. Most notable among these were Filamin A, RhoGDIα, SPARC, hnRNPH2, and PRDX2.

CONCLUSIONS AND SIGNIFICANCE

This systems-level approach sheds new light on the molecular networks underlying PRL-1 action and presents several novel directions for future, hypothesis-based studies.

The regulatory function of SPARC in vascular biology

SPARC is a matricellular protein, able to modulate cell/ECM interactions and influence cell responses to growth factors, and therefore is particularly attuned to contribute to physiological processes involving changes in ECM and cell mobilization. Indeed, the list of biological processes affected by SPARC includes wound healing, tumor progression, bone formation, fibrosis, and angiogenesis. The process of angiogenesis is complex and involves a number of cellular processes such as endothelial cell proliferation, migration, ECM degradation, and synthesis, as well as pericyte recruitment to stabilize nascent vessels. In this review, we will summarize current results that explore the function of SPARC in the regulation of angiogenic events with a particular emphasis on the modulation of growth factor activity by SPARC in the context of blood vessel formation. The primary function of SPARC in angiogenesis remains unclear, as SPARC activity in some circumstances promotes angiogenesis and in others is more consistent with an anti-angiogenic activity. Undoubtedly, the mercurial nature of SPARC belies a redundancy of functional proteins in angiogenesis as well as cell-type-specific activities that alter signal transduction events in response to unique cellular milieus. Nonetheless, the investigation of cellular mechanisms that define functional activities of SPARC continue to contribute novel and exciting paradigms to vascular biology.

Pulp Healing and Regeneration

Differences between pulp repair and regeneration guide different strategic options. After mild carious dentin lesions, odontoblasts and Hoehl’s cells are implicated in the formation of reactionary dentin. Reparative dentin formation and/or pulp regeneration after partial degradation is under the control of pulp progenitors. A series of questions arise from recent researches on tissue engineering. In this series of questions, we compare the therapeutic potential of pluripotent embryonic and adult stem cells, both being used in cell-based dental therapies. Crucial questions arise on the origin of stem cells and the localization of niches of progenitors in adult teeth. Circulating progenitor cells may also be candidate for promoting pulp regeneration. Then, we focus on strategies allowing efficient progenitors recruitment. Along this line, we compare the potential of embryonic stem cells versus adult stem cells. Re-programming adult pulp cells to become induced pluripotent stem cells constitute another option. Genes, transcription factors and growth factors may be used to stimulate the differentiation cascade. Extracellular matrix molecules or some bioactive specific domains after enzymatic cleavage may also contribute to the formation of an artificial pulp and ultimately to its mineralization.

Dasatinib reduces FAK phosphorylation increasing the effects of RPI-1 inhibition in a RET/PTC1-expressing cell line

Background

TPC-1 is a papillary thyroid carcinoma (PTC)-derived cell line that spontaneously expresses the oncogene RET/PTC1. TPC-1 treated with the RET/PTC1 inhibitor RPI-1 displayed a cytostatic and reversible inhibition of cell proliferation and a strong activation of focal adhesion kinase (FAK). As dasatinib inhibition of Src results in reduction of FAK activation, we evaluated the effects of TPC-1 treatment with dasatinib in combination with RPI-1.

Results

Dasatinib (100 nM) strongly reduced TPC-1 proliferation and induced marked changes in TPC-1 morphology. Cells appeared smaller and more contracted, with decreased cell spreading, due to the inhibition of phosphorylation of important cytoskeletal proteins (p130^CAS, Crk, and paxillin) by dasatinib. The combination of RPI-1 with dasatinib demonstrated enhanced effects on cell proliferation (more than 80% reduction) and on the phosphotyrosine protein profile. In particular, RPI-1 reduced the phosphorylation of RET, MET, DCDB2, CTND1, and PLCγ, while dasatinib acted on the phosphorylation of EGFR, EPHA2, and DOK1. Moreover, dasatinib completely abrogated the phosphorylation of FAK at all tyrosine sites (Y576, Y577, Y861, Y925) with the exception of the autoactivation site (Y397). Notably, the pharmacological treatments induced an overexpression of integrin β1 (ITB1) that was correlated with a mild enhancement in phosphorylation of ERK1/2 and STAT3, known for their roles in prevention of apoptosis and in increase of proliferation and survival. A reduction in Akt, p38 and JNK1/2 activation was observed.

Conclusions

All data demonstrate that the combination of the two drugs effectively reduced cell proliferation (by more than 80%), significantly decreased Tyr phosphorylation of almost all phosphorylable proteins, and altered the morphology of the cells, supporting high cytostatic effects. Following the combined treatment, cell survival pathways appeared to be mediated by STAT3 and ERK activities resulting from integrin clustering and FAK autophosphorylation. EphA2 may also contribute, at least in part, to integrin and FAK activation. In conclusion, these data implicate ITB1 and EphA2 as promising therapeutic targets in PTC.

SPARC/osteonectin functions to maintain homeostasis of the collagenous extracellular matrix in the periodontal ligament

Expression of secreted protein acidic and rich in cysteine (SPARC)/osteonectin, a collagen-binding matricellular protein, is frequently associated with tissues with high rates of collagen turnover, such as bone. In the oral cavity, expression of SPARC/osteonectin has been localized to the periodontal ligament (PDL), a collagen-rich tissue with high rates of collagen turnover. The PDL is critical for tooth position within the alveolar bone and for absorbing forces generated by chewing. To characterize the function of SPARC/osteonectin in PDL, SPARC/osteonectin expression in murine PDL was evaluated by immunochemistry at 1, 4, 6, and >18 months. Highest levels of SPARC/osteonectin were detected at 1 and >18 months, with decreased levels associated with adult (4-6 months) PDL. To determine whether the absence of SPARC/osteonectin expression influenced cellular and fibrillar collagen content in PDL, PDL of SPARC-null mice was evaluated using histological stains and compared with that of wild-type (WT). Our results demonstrated decreased numbers of nuclei in PDL of SPARC-null mice at 1 month. In addition, decreased collagen volume fractions were found at 1 and >18 months and decreases in thick collagen fiber volume fraction were detected at 4, 6, and >18 months in SPARC-null PDL. The greatest differences in cell number and in collagen content between SPARC-null and WT PDL coincided with ages at which levels of SPARC/osteonectin expression were highest in WT PDL, at 1 and >18 months. These results support the hypothesis that SPARC/osteonectin is critical in the control of tissue collagen content and indicate that SPARC/osteonectin is necessary for PDL homeostasis.

Modulation of matrix remodeling by SPARC in neoplastic progression

SPARC is a matricellular glycoprotein that mediates interactions between cells and their microenvironment. It is produced at sites of tissue remodeling, where it regulates matrix deposition and turnover, cell adhesion, and signaling by extracellular factors, exerting profound effects on tissue architecture and cell physiology. During extensive matrix remodeling in neoplastic progression, SPARC is expressed in cancer-associated stroma and in malignant cells of some types, affecting tumor development, invasion, metastases, angiogenesis and inflammation. SPARC-induced changes in the tumor microenvironment can suppress or promote progression of different cancers depending on the tissue and cell type. Understanding the mechanism of matrix remodeling and its regulation by SPARC is essential for the development of new treatment strategies for highly aggressive cancers.