The Regulation Of Glioma Stem Cell Proliferation And Differentiation By Architectural Transcription Factors HMGA1 And HMGA2

Astrocytoma, also known as glioma, is the most common primary brain tumor. One of the most aggressive and malignant form of glioma is glioblastoma multiforme(GBM), which showed poor therapy responses and prognosis, and the median survival of GBM patients is only about 12 to 15 months. Recent studies demonstrated that glioma stem cells (GSCs) are responsible for tumorigenesis and recurrence. The existence of such cells can enhance glioma resistance to radiation and chemotherapy, thus studies regarding properties of glioma stem cell is essential for developing new therapeutic means. HMGA1 and HMGA2, two architectural transcription factors, were essential for maintaining the open chromatin state of neural precursor cells (NPCs) in mouse cortical development. Subsequent studies found these "stemnness" factors also play a key role in tumorigenesis of multiple benign and malignant tumors. The correlation between HMGA expression levels and mesenchymal phenotype made it important to determine their roles in tumor invasion and metastasis. Both HMGA1 and HMGA2 have been reported expressed in glioma, and their expression levels correlate with tumor grades.Here, we found that HMGA1 and HMGA2 expressed higher in glioma tissue than in normal brains using immunohistochemical staining of glioma tissue arrays. The expression of the HMGA2 area and density positively correlated with tumor grades. TCGA data analysis also showed that HMGA2 expressed at significantly high level in mesenchymal subtype of glioblastoma, which showed poorer prognosis compared with other subtypes, while the expression of HMGA1 did not show preference among GBM subtypes. Using immunofluorescence staining, we found that most HMGA1 positive cells also express SOX2 protein, a marker for GSCs, whereas the HMGA2 labels both SOX2-positive cells and tumor vascular smooth muscle cells (pericytes).To study roles of HMGA2 proteins in cell fate determination of glioma stem cells, we enriched GSCs from glioblastoma. In the presence of mitogens, GSCs depleted of HMGA1 or HMGA2 had markedly impaired proliferation and spherogenic capability, indicating HMGA1 and HMGA2 play an important role in sustaining the sternness of glioma stem cells. In addition, HMGA2 can enhance the mesenchymal differentiation of glioma stem cells and blood vessels formation under differentiation condition and cytokines stimulation. Knockdown of HMGA2 can significantly inhibit pericyte and blood vessel formation of GSCs, which is consistent with intracranial xenograft experiments. In vitro transwell migration, invasion and coculture with HUVEC assays also proved that knockdown of HMGA2 can restrain the mesenchymal transition and pericyte formation of glioma stem cells. Through RNA-seq transcriptome analyses, we found both HMGA1 and HMGA2 positively regulate the expression of proliferation and cell-cycle related gene. In addition, HMGA2 specifically regulate a few mesenchymal differentiation and pericyte associated genes, including FOXM1, PLAU and CRY61, which may be essential for tumor initiation and metastasis.To sum up, our observations suggest that both HMGA1 and HMGA2 were able to maintain the stemness of GSCs, similar to their functions in the NPCs. Further, HMGA2 was able to effectively enhance the mesenchymal transformation of glioma stem cells and vascular pericyte formation. These studies expand our knowledge on GSC properties, and may provide novel clues in therapeutically targeting GSCs.