Michael Clarke lab
In addition to his clinical duties in the division of Oncology, Dr. Clarke maintains a laboratory focused on two areas of research: i) the control of self-renewal of normal stem cells and their malignant counterparts; and ii) the identification and characterization of cancer stem cells. A central issue in stem cell biology is to understand the mechanisms that regulate self-renewal of hematopoietic stem cells, which are required for hematopoiesis to persist for the lifetime of the animal. Until recently, the molecular mechanisms that regulate adult stem cell self-renewal were not known. His laboratory recently found that the proto-oncogene Bmi-1 regulates stem cell self-renewal via an epigenetic mechanism. By investigating the pathways upstream and downstream of Bmi1, the laboratory is actively investigating the molecular pathways that regulate self-renewal.
Cancers arise as a result of a series of genetic mutations. A better understanding of the consequences of these mutations on the underlying biology of the neoplastic cells will help to focus the development of more effective therapies. Solid tumors such as breast cancers contain heterogeneous populations of neoplastic cells. Dr. Clarkes group has developed a technique that allows the isolation and characterization of tumorigenic and non-tumorigenic populations of cancer cells present in human breast, colon and head and neck cancer tumors. Only a small minority of cancer cells had the capacity to form new tumors in a xenograft model. This tumorigenic cell population could be identified prospectively and consistently had definable and identical phenotype. The tumorigenic cells displayed stem cell-like properties in that they were capable of generating new tumors containing additional stem cells as well as regenerating the phenotypically mixed populations of non-tumorigenic cells present in the original tumor. Effective treatment of cancer will require therapeutic strategies that are able to target and eliminate this tumorigenic subset of cells. The laboratory is pursuing the identification of cancer stem cells in other tumors so that they can be studied. Dr. Clarkes laboratory will provide other members of the program with the expertise to identify and isolate cancer stem cells from solid tumors of epithelial origin. Finally, the laboratory is actively pursuing how cancer stem cells self-renew to maintain themselves and escape the genetic constraints on unlimited self-renewal that regulate normal stem cell numbers. Differences in self-renewal pathways between normal and malignant stem cells could be targeted by new therapeutic agents to eliminate cancer stem cells.
A Quiescent Bcl11b High Stem Cell Population Is Required for Maintenance of the Mammary Gland.
Cell stem cell
2017; 20 (2): 247-260 e5
Stem cells in many tissues sustain themselves by entering a quiescent state to avoid genomic insults and to prevent exhaustion caused by excessive proliferation. In the mammary gland, the identity and characteristics of quiescent epithelial stem cells are not clear. Here, we identify a quiescent mammary epithelial cell population expressing high levels of Bcl11b and located at the interface between luminal and basal cells. Bcl11b(high) cells are enriched for cells that can regenerate mammary glands in secondary transplants. Loss of Bcl11b leads to a Cdkn2a-dependent exhaustion of ductal epithelium and loss of epithelial cell regenerative capacity. Gain- and loss-of-function studies show that Bcl11b induces cells to enter the G0 phase of the cell cycle and become quiescent. Taken together, these results suggest that Bcl11b acts as a central intrinsic regulator of mammary epithelial stem cell quiescence and exhaustion and is necessary for long-term maintenance of the mammary gland.
View details for DOI 10.1016/j.stem.2016.11.007
View details for PubMedID 28041896
View details for PubMedCentralID PMC5341693
- CDX2 as a Prognostic Biomarker in Stage II and Stage III Colon Cancer NEW ENGLAND JOURNAL OF MEDICINE 2016; 374 (3): 211-222 Hide More
A cell-intrinsic role for TLR2-MYD88 in intestinal and breast epithelia and oncogenesis.
Nature cell biology
2014; 16 (12): 1238-1248
It has been postulated that there is a link between inflammation and cancer. Here we describe a role for cell-intrinsic toll-like receptor-2 (TLR2; which is involved in inflammatory response) signalling in normal intestinal and mammary epithelial cells and oncogenesis. The downstream effectors of TLR2 are expressed by normal intestinal and mammary epithelia, including the stem/progenitor cells. Deletion of MYD88 or TLR2 in the intestinal epithelium markedly reduces DSS-induced colitis regeneration and spontaneous tumour development in mice. Limiting dilution transplantations of breast epithelial cells devoid of TLR2 or MYD88 revealed a significant decrease in mammary repopulating unit frequency compared with the control. Inhibition of TLR2, its co-receptor CD14, or its downstream targets MYD88 and IRAK1 inhibits growth of human breast cancers in vitro and in vivo. These results suggest that inhibitors of the TLR2 pathway merit investigation as possible therapeutic and chemoprevention agents.
View details for DOI 10.1038/ncb3058
View details for PubMedID 25362351
Usp16 contributes to somatic stem-cell defects in Down's syndrome.
2013; 501 (7467): 380-384
Down's syndrome results from full or partial trisomy of chromosome 21. However, the consequences of the underlying gene-dosage imbalance on adult tissues remain poorly understood. Here we show that in Ts65Dn mice, which are trisomic for 132 genes homologous to genes on human chromosome 21, triplication of Usp16 reduces the self-renewal of haematopoietic stem cells and the expansion of mammary epithelial cells, neural progenitors and fibroblasts. In addition, Usp16 is associated with decreased ubiquitination of Cdkn2a and accelerated senescence in Ts65Dn fibroblasts. Usp16 can remove ubiquitin from histone H2A on lysine 119, a critical mark for the maintenance of multiple somatic tissues. Downregulation of Usp16, either by mutation of a single normal Usp16 allele or by short interfering RNAs, largely rescues all of these defects. Furthermore, in human tissues overexpression of USP16 reduces the expansion of normal fibroblasts and postnatal neural progenitors, whereas downregulation of USP16 partially rescues the proliferation defects of Down's syndrome fibroblasts. Taken together, these results suggest that USP16 has an important role in antagonizing the self-renewal and/or senescence pathways in Down's syndrome and could serve as an attractive target to ameliorate some of the associated pathologies.
View details for DOI 10.1038/nature12530
View details for PubMedID 24025767
View details for PubMedCentralID PMC3816928
Identification of a cKit(+) Colonic Crypt Base Secretory Cell That Supports Lgr5(+) Stem Cells in Mice
2012; 142 (5): 1195-?
Paneth cells contribute to the small intestinal niche of Lgr5(+) stem cells. Although the colon also contains Lgr5(+) stem cells, it does not contain Paneth cells. We investigated the existence of colonic Paneth-like cells that have a distinct transcriptional signature and support Lgr5(+) stem cells.We used multicolor fluorescence-activated cell sorting to isolate different subregions of colon crypts, based on known markers, from dissociated colonic epithelium of mice. We performed multiplexed single-cell gene expression analysis with quantitative reverse transcriptase polymerase chain reaction followed by hierarchical clustering analysis to characterize distinct cell types. We used immunostaining and fluorescence-activated cell sorting analyses with in vivo administration of a Notch inhibitor and in vitro organoid cultures to characterize different cell types.Multicolor fluorescence-activated cell sorting could isolate distinct regions of colonic crypts. Four major epithelial subtypes or transcriptional states were revealed by gene expression analysis of selected populations of single cells. One of these, the goblet cells, contained a distinct cKit/CD117(+) crypt base subpopulation that expressed Dll1, Dll4, and epidermal growth factor, similar to Paneth cells, which were also marked by cKit. In the colon, cKit(+) goblet cells were interdigitated with Lgr5(+) stem cells. In vivo, this colonic cKit(+) population was regulated by Notch signaling; administration of a γ-secretase inhibitor to mice increased the number of cKit(+) cells. When isolated from mouse colon, cKit(+) cells promoted formation of organoids from Lgr5(+) stem cells, which expressed Kitl/stem cell factor, the ligand for cKit. When organoids were depleted of cKit(+) cells using a toxin-conjugated antibody, organoid formation decreased.cKit marks small intestinal Paneth cells and a subset of colonic goblet cells that are regulated by Notch signaling and support Lgr5(+) stem cells.
View details for DOI 10.1053/j.gastro.2012.02.006
View details for Web of Science ID 000303113600038
View details for PubMedID 22333952
View details for PubMedCentralID PMC3911891