Nerlov Group (Visiting)
Transcription factor function in development, physiology and disease
Defective keratinocyte differentiation and epidermal hyperplasia upon conditional ablation of C/EBPα and C/EBPβ expression in the skin. A) Skin sections from control mice (carrying floxed alleles of both C/EBPα and β, but not the keratin 14-Cre transgene; upper panel) and C/EBPα/β double knockout mice (lower panel. As above, but with the K14-Cre transgene). The sections were stained with antibodies against the basal cell marker (keratin 14, green), a marker for differentiating keratinocytes (keratin 10, red) and the DNA stain DAPI (blue). The lower boundary of the epidermis is defined by the keratin 14 positive basal cells; the outer surface of the skin is at the top of the panels. Note the expansion of the keratin 14 expression domain and diminished keratin 10 expression in double knockout mice. B) Skin sections as in A), stained with antibodies against keratin 14 (green) and proliferating cell nuclear antigen (PCNA, a marker of proliferating cells; red). Note the expanded domain of cell proliferation in double knockout mice.
Transcription factors play important roles in regulation of cellular proliferation, differentiation and in the function of fully differentiated cells. We look at how transcription factors link the processes of cellular differentiation and self-renewal/proliferation, both at the stem cell level and during terminal cellular differentiation. We use mouse genetics to study in vivo the C/EBP family of basic regionleucine zipper transcription factors, proteins which play essential roles in the development of the hematopoietic system, adipose tissues, epithelia and granulosa cells. We use conditional mutagenesis to delete one or more C/EBPs from specific cell types, and point mutagenesis to specifically alter C/EBP protein-protein interactions or post-translational modifications.
Previous and current research
We previously defined E2F repression and interaction with the SWI/SNF complex as C/EBPα functions essential for adipose and myeloid differentiation (Pedersen et al., 2001, Genes & Dev. 15; Porse et al., 2001, Cell, 107). We have now found that E2F repression is required also for myeloid tumour suppression, as mice homozygous for mutations that disable C/EBPα-E2F interaction have increased myeloid progenitor proliferation and develop an acute myeloid leukemia (AML)-like disease (Porse et al., 2005). In contrast, we did not observe any effect on progenitor proliferation upon deletion of the Cdk2/Cdk4 interaction domain of C/EBPα (Porse et al., 2006). Mutations in the gene encoding C/EBPα are found in AML patients, and the most common type results in specific loss of the 42kDa C/EBPα isoform (p42), while preserving expression of the 30kDa isoform (p30). Only p42 has E2F repression activity, and when we generated p42 knockout mice we found that also these developed AML. We are now generating knockin mice with other AML-derived mutations, and investigating the role of C/EBPα mutations in the formation of self-renewing leukemic stem cells. We are currently investigating the role of C/EBPs in keratinocytes, and have observed a similar role for C/EBPs in the transition from proliferation to differentiation; however, in this case C/EBPα and C/EBPβ function redundantly, and removal of both is necessary to cause keratinocyte hyperproliferation and impair their differentiation (see figure). Other main projects involve studying the role of post-translational modifications of C/EBPs in metabolism and macrophage activation, and the transcriptional regulation of C/EBPβ.
Future projects and goals
The future focus of the laboratory will be to elucidate the molecular mechanisms by which C/EBPs control differentiation in non-hematopoietic tissues (neurons, skin, liver), and to determine the signalling pathways that regulate C/EBPs through post-translational modification. A major effort will deal with the effects of leukemogenic mutations on hematopoietic stem cell function, in order to determine how malignant, self-renewing tumour stem cells arise.