Cellular differentiation is accompanied by dramatic changes in chromatin
structure which are associated with the activation of lineage-specific transcriptional
programs. Facilitates Chromatin Transcription (FACT) is a histone chaperone
complex which is important for chromatin-associated processes such as transcription,
DNA replication and DNA repair. However, the role of FACT during differentiation of
undifferentiated or stem-cell like cells has not yet been elucidated. We investigated
the role of the FACT component Structure Specific Recognition Protein 1 (SSRP1) in
adipocyte and osteoblast differentiation. Depletion of SSRP1 in human
mesenchymal stem cells (hMSC) elicited lineage-specific effects where the
adipocyte-specific genes PPARG, RASD1 and PDK4 were significantly increased
while markers of osteoblast differentiation markedly decreased. Consistently, Oil Red
O staining was increased during adipocyte differentiation while alkaline phosphatase
staining was decreased in osteoblast differentiation following knockdown of SSRP1.
Osteoblast differentiation plays a pivotal role in maintenance of bone
homeostasis important for different bone-associated diseases including age-related
bone loss. Thus this study was further focused on the molecular regulation of
SSRP1-mediated effects on osteoblast differentiation. Transcriptome-wide RNA-seq
revealed a specific enrichment of down-regulation of the canonical Wnt signaling
pathway following SSRP1 depletion in osteoblasts. Furthermore a number of
biological processes important for osteoblast differentiation including glycosylation,
cell-cell contact, adhesion, extra cellular matrix, ossification, osteoblast differentiation,
bone and skeletal development were affected by SSRP1 knockdown. In addition a
significant nuclear co-localization of SSRP1 and β-catenin was observed where
depletion of SSRP1 diminished accumulation of active β-catenin in the nucleus.
Together, our data suggest a previously unknown specific role for SSRP1 in
promoting the activation of canonical Wnt signaling during lineage-specific
differentiation
