NANOG and brain neoplasm: Considering Elk-1 was previously shown to regulate CD133 expression [15], we have also studied Elk-1 expression levels in CD133− and CD133+ cell lines as well as primary brain tumors, indicating Elk-1 was indeed overexpressed in CD133+ cells, and when Elk-1 expression was silenced by RNAi, SOX2, and NANOG expression were reduced in both CD133+ primary GBMs, as well as CD133+ cell lines in a cell context-dependent manner.