Claudio Basilico, MD
Professor and Chair of Microbiology
M.D. 1960 University of Milan
Cancer Stem Cells, Adult Stem Cells
signal transduction, Cell-cycle, Growth Factors, Oncogenes, Bone Development, Cancer Stem Cells
New York University School of Medicine
550 First Avenue, MSB 256
New York, NY, 10016
Tel: (212) 263-5341
The major interest of my laboratory is the control of proliferation in normal and cancer cells and the genes and gene-products whose interplay regulates proliferation and differentiation.
To understand how growth factor signaling promotes cell proliferation and differentiation, we are studying the mechanism of action and the regulation of expression of fibroblast growth factors (FGF). FGF represents a large family of growth factors which signal through their interaction with tyrosine kinase receptors (FGFR) which also make-up a gene family. FGF signaling plays a major role in a variety of developmental processes. Ectopic or excessive FGF expression can lead to oncogenesis. The main projects presently being carried out focus on the regulation of skeletal development by FGF signaling. Unregulated FGF signaling, due to FGFR activating mutations, causes a variety of dominant bone morphogenetic disorders in humans, including several forms of dwarfism and craniosynostosis syndromes. Excessive FGF signaling alters bone development by affecting the dynamics of growth and differentiation of chondrocytes and osteoblasts, the two major cell types involved in bone formation. We are studying the biological response of these two cell types to FGF and the key pathways involved in this process.
In chondrocytes, we found that FGF signaling inhibits proliferation and increases apoptosis both in vitro and in vivo. These effects are cell type-specific since FGFs induce proliferation in most other cell types, and provide a logical explanation of why excessive FGF signaling causes dwarfism and chondrodysplastic syndromes. FGFs induce in chondrocytes a complex network of signaling and transcriptional events which ultimately result in growth arrest and induction of several aspects of chondrocytes hypertrophic differentiation. We have shown that FGF-induced growth arrest requires the activity of two Retinoblastoma (Rb) family members, p107 and p130, but not Rb itself. One of the earliest distinguishing events following FGF treatment is the very rapid dephosphorylation of p107. We have shown that p107 dephosphorylation is a critical early event in the growth-inhibitory response of these cells to FGF signaling and that the PP2A phosphatase targets p107 for dephosphorylation in FGF-treated chondrocytes. We have recently determined that the B55 alpha regulatory subunit of PP2A is activated by FGF to target this enzyme to p107.
Immature osteoblasts respond to FGF with increased proliferation, while differentiating cells undergo apoptosis. Sustained FGF signaling inhibits differentiation. We have examined the program of gene expression in osteoblasts expressing activated FGFR mutants and detected a significant down-regulation of Wnt target gene expression. Concomitantly, we have observed a dramatic induction of expression of Sox2, a transcription factor of the HMG domain family, whose expression is a classical marker of embryonic stem cells. Sox2 is also induced by FGF treatment of normal osteoblasts and is clearly detectable in cranial osteoblasts in vivo. Wnt signaling promotes osteoblast function and high bone mass in humans and mice and thus inhibition of Wnt signaling is likely to be one important mechanism by which FGFs inhibit osteoblast differentiation. Our results showed that FGF utilizes multiple mechanisms to inhibit Wnt-induced transcription in osteoblasts and that Sox2 induction plays a major role since this protein can bind to β-catenin and inhibits its transcriptional activity. Indeed Sox2 overexpression can by itself inhibit osteoblast differentiation.
While investigating the role of Sox2 induction in the osteoblast response to FGF we have made the exciting discovery that Sox2 is required for self-renewal of the osteoblast lineage. Inactivation of Sox2 in cultured osteoblasts abolish proliferation capacity and cause these cells to enter a senescent-like phenotype. Conditional KO of Sox2 in the osteoblast lineage in mice produces animals which are small, osteopenic and have low bone density. Sox2 is highly expressed in osteospheres, thought to represent multipotent or unipotent stem cells in the osteoblast lineage. Sox2 maintains a proliferative stem-like state in osteoblasts by activating transcription of critical target “stemness” genes and by inhibiting the activity of the prodifferentiation Wnt pathway, using both transcriptional and post-transcriptional mechanisms. Importantly, Sox2 plays a similar role in osteosarcomas, where Sox2 downregulation abolishes tumorigenicity, promotes osteogenic differentiation and activate the Wnt pathway. This indicates that in these tumors, high Sox2 expression sustains a population of cancer stem cells.
We have identified the Key genes that determine the requirement for Sox2 in the osteoblastic lineage. The osteoblastic and adipocytic lineages are alternative fates that arise from mesenchymal stem cells (MSCs). Sox2, and YAP, the Hippo pathway effector, regulate self-renewal and early fate decisions in these lineages. Sox2 directly regulates YAP expression that can compensate for the self-renewal defect caused by Sox2 inactivation. Increased Sox2 or YAP expression inhibits osteogenesis, while depleting either one accelerates it. Sox2 strongly favors adipogenesis and induces PPARγ, but adipogenesis can only occur within physiological levels of YAP expression, as both YAP overexpression or depletion inhibit the process. We also show that YAP binds b-catenin and directly induces the Wnt antagonist Dkk1, to dampen potent pro-osteogenic Wnt signals.
These findings highlight a previously unknown Hippo-independent regulation of YAP by Sox2 that cooperatively antagonize the Wnt/b-catenin pathway and regulate PPARγ to determine osteogenic or adipocytic fates.
An even broader antagonism of the tumor suppressive Hippo pathway by Sox2 takes place in osteosarcomas. In these tumors Sox2 also induces YAP1 expression, but additionally downregulates Merlin (Nf2), a positive Hippo regulator. High YAP1 and low Merlin expression mark the subpopulation of osteosarcoma cells we have identified as cancer stem cells.
- Murtha, M., Wang, Y., Basilico, C., Dailey, L. Isolation and analysis of DNA derived from nucleosome-free regions. Methods Mol Biol. 2013;977:35-51. PMID: 23436352
- Kolupaeva V., Daempfling L., Basilico C., 157. The B55 alpha regulatory subunit of Protein Phosphatase 2A mediates FGF-induced p107 dephosphorylation and growth arrest in chondrocytes. Mol Cell Biol. 2013 Aug;33(15):2865-78. PMID: 23716589
- Seo E., Basu-Roy U., Gunaratne P. H., Coarfa C., Lim DS, Basilico C., Mansukhani A., Sox2 regulates YAP1 to maintain stemness and determine cell fate in the osteo-adipo lineage. Cell, 2013 Jun 27;3(6):2075-87. PMID: 23791527
- Basu-Roy U, Seo E, Ramanathapuram L, Rapp TB, Perry JA, Orkin SH, Mansukhani A, Basilico C. Sox2 maintains self renewal of tumor-initiating cells in osteosarcomas. Oncogene. 2012 May 3;31(18):2270-82. PMID: 21927024
- Deckelbaum RA, Holmes G, Zhao Z, Tong C, Basilico C, Loomis CA. Regulation of cranial morphogenesis and cell fate at the neural crest-mesoderm boundary by engrailed 1. Development. 2012 Apr;139(7):1346-58. PMID: 22395741
- Basu-Roy U, Basilico C, Mansukhani A. Perspectives on cancer stem cells in osteosarcoma. Cancer Lett. 2012 May 29. PMID: 22659734
- Holmes G, Basilico C. Mesodermal expression of Fgfr2(S252W) is necessary and sufficient to induce craniosynostosis in a mouse model of Apert syndrome. Dev Biol. 2012 Aug 15368(2):283-93. PMID: 22664175
- Kolupaeva, V., Basilico C. Overexpression of cyclin E/CDK2 complexes overcomes FGF-induced cell cycle arrest in the presence of hypophosphorylated Rb proteins. Cell Cycle. 2012 Jul 1;11(13):2557-66. PMID: 22713240
- Seo E, BasuRoy U, Zavadil J, Basilico C, Mansukhani A. Distinct functions of Sox2 control self-renewal and differentiation in the osteoblast lineage. Mol Cell Biol. 2011 Nov 31: 4593-4608. PMID: 21930787
- Holmes G, Bromage TG, Basilico C. The Sox2 high mobility group transcription factor inhibits mature osteoblast function in transgenic mice. Bone. 2011 Oct;49(4):653-61. PMID: 21703370
- Basu-Roy U, Ambrosetti D, Favaro R, Nicolis SK, Manukhani A, Basilico C. The transcription factor Sox2 is required for osteoblast self-renewal. Cell Death Differ. 2010 Aug;17(8):1345-53. PMID: 20489730
- Tran T, Kolupaeva V, Basilico C. FGF inhibits the activity of the cyclin B1/CDK1 kinase to induce a transient G₂arrest in RCS chondrocytes.Cell Cycle. 2010 Nov 1;9(21):4379-86. PMID: 21051949
- Holmes G, Rothschild G, Roy UB, Deng CX, Mansukhani A, Basilico C. Early onset of craniosynostosis in an Apert mouse model reveals critical features of this pathology. Dev Biol. 2009 Apr 15;328(2):273-84. PMID: 19389359
- Yaragatti M, Basilico C, Dailey L. Identification of active transcriptional regulatory modules by the functional assay of DNA from nucleosome-free regions. Genome Res. 2008 Jun;18(6):930-8. PMID: 18441229
- Ambrosetti D, Holmes G, Mansukhani A, Basilico C. Fibroblast growth factor signaling uses multiple mechanisms to inhibit Wnt-induced transcription in osteoblasts. Mol Cell Biol. 2008 Aug;28(15):4759-71. PMID: 18505824
- Kolupaeva V, Laplantine E, Basilico C. PP2A-mediated dephosphorylation of p107 plays a critical role in chondrocyte cell cycle arrest by FGF. PLoS One. 2008;3(10):e3447. PMID: 18927618