HOXA5/Galectin-1 Regulation of Brain Tumour Stem Cells

Abstract

Glioblastoma (GB) is the most aggressive primary brain tumour in adults, with a median survival of 15 months following maximal surgical resection, ionizing radiation (IR), and temozolomide (TMZ) chemotherapy. Tumour recurrence is largely driven by brain tumour stem cells (BTSCs), a specialized population of cells in GB tumours that exhibit persistent self-renewal, proliferation, and therapeutic resistance, driving tumour recurrence following treatment. Thus, a deeper understanding of the molecular mechanisms regulating BTSCs is essential for the development of novel therapeutic strategies aimed at improving long-term patient survival.

The galectin-1/homeobox A5 (HOXA5) signalling has been implicated in sustaining BTSC stemness and tumourigenic transcriptional programs, yet the precise mechanisms by which galectin-1 regulates HOXA5's function remain unclear. Galectin-1 primarily functions as a non-covalent homodimer, and structural docking models predict that homodimeric galectin-1 interacts with the N-terminal region of HOXA5 to promote DNA binding, whereas monomeric galectin-1 may impede DNA binding by directly interacting with the homeodomain.

To assess the docking model which predicts that galectin-1 dimerization is necessary for HOXA5's regulatory functions, we generated plasmids encoding either wild-type (WT) homodimeric galectin-1 or a dimerization-deficient mutant (Mut) and expressed them in patient-derived BTSCs via electroporation. Analysis conducted in three genetically distinct BTSC lines revealed that WT galectin-1 enhanced BTSC self-renewal and sphere-forming capacity, whereas the Mut galectin-1 consistently attenuated stemness and growth. Complementary chromatin immunoprecipitation-quantitative PCR (ChIP-qPCR) experiments in human embryonic kidney 293T (HEK293T) cells co-expressing HOXA5 and either galectin-1 WT or Mut revealed that the Mut was associated with reduced HOXA5 enrichment at the promoters of key target genes compared to WT. These findings support a model in which galectin-1 dimerization promotes HOXA5 chromatin binding and transcriptional regulation of genes critical for BTSC maintenance. Thus, targeting galectin-1's oligomeric state may be a potential novel therapeutic strategy for disrupting BTSC-driven GB recurrence.