Biomedical subjects

Keith Brennan

Publications and source records attributed to Keith Brennan.

8 recordsLinked to original sources

PubMed2006

Aberrant activation of notch signaling in human breast cancer.

A role for Notch signaling in human breast cancer has been suggested by both the development of adenocarcinomas in the murine mammary gland following pathway activation and the loss of Numb expression, a negative regulator of the Notch pathway, in a large proportion of breast carcinomas. However, it is not clear currently whether Notch signaling is frequently activated in breast tumors, and how it causes cellular transformation. Here, we show accumulation of the intracellular domain of Notch1 and hence increased Notch signaling in a wide variety of human breast carcinomas. In addition, we show that increased RBP-Jkappa-dependent Notch signaling is sufficient to transform normal breast epithelial cells and that the mechanism of transformation is most likely through the suppression of apoptosis. More significantly, we show that attenuation of Notch signaling reverts the transformed phenotype of human breast cancer cell lines, suggesting that inhibition of Notch signaling may be a therapeutic strategy for this disease.

Apoptosis↗

PubMed2006

Notch receptor encodes two structurally separable functions in Drosophila: a genetic analysis.

The Notch gene of Drosophila encodes a single transmembrane receptor that plays a central role in the process of lateral inhibition. This process results in the selection of individual mesodermal and neural precursors during the development of the muscular and nervous systems. The activation of Notch during lateral inhibition is mediated by the transmembrane ligand Delta (Dl) and effected by the transcription factor Suppressor of Hairless (Su(H)). The same functional cassette plays a role in other processes, in particular, the development and patterning of the wing. Genetic analysis has suggested that, in addition to the Su(H)-dependent pathway, Notch can signal in an Su(H)-independent manner. This process seems to be tightly associated with signalling by Wingless, a member of the Wnt family of signalling molecules. Here, we have analyzed further the possibility that the Notch protein encodes two different functions. To do so, we have studied the activities and genetic properties of different Notch receptors bearing deletions of specific regions of the intracellular and the extracellular domains in different developmental processes, and have sought to correlate the activity of these mutant proteins with those of existing mutants in Notch. Our results support the existence of at least two different activities of Notch each of which can be associated with specific structural domains.

Animals↗

PubMed2005

Notch modulates Wnt signalling by associating with Armadillo/beta-catenin and regulating its transcriptional activity.

The establishment and stability of cell fates during development depend on the integration of multiple signals, which ultimately modulate specific patterns of gene expression. While there is ample evidence for this integration at the level of gene regulatory sequences, little is known about its operation at other levels of cellular activity. Wnt and Notch signalling are important elements of the circuitry that regulates gene expression in development and disease. Genetic analysis has suggested that in addition to convergence on the transcription of specific genes, there are modulatory cross-regulatory interactions between these signalling pathways. We report that the nodal point of these interactions is an activity of Notch that regulates the activity and the amount of the active/oncogenic form of Armadillo/beta-catenin. This activity of Notch is independent of that induced upon cleavage of its intracellular domain and which mediates transcription through Su(H)/CBF1. The modulatory function of Notch described here, contributes to the establishment of a robust threshold for Wnt signalling which is likely to play important roles in both normal and pathological situations.

Animals↗

PubMed2005

Desmosomal cadherin misexpression alters beta-catenin stability and epidermal differentiation.

Desmosomal adhesion is important for the integrity and protective barrier function of the epidermis and is disregulated during carcinogenesis. Strong adhesion between keratinocytes is conferred by the desmosomal cadherins, desmocollin (Dsc) and desmoglein. These constitute two gene families, members of which are differentially expressed in epidermal strata. It has been suggested that this stratum-specific expression regulates keratinocyte differentiation. We tested this hypothesis by misdirecting the expression of the basally abundant desmosomal cadherins Dsc3a and Dsc3b to suprabasal differentiating keratinocytes in transgenic mice. No phenotype was apparent until adulthood, when mice developed variable ventral alopecia and had altered keratinocyte differentiation within affected areas. The follicular changes were reminiscent of changes in transgenic mice with an altered beta-catenin stability. Stabilized beta-catenin and increased beta-catenin transcriptional activity were demonstrated in transgenic mice prior to the phenotypic change and in transgenic keratinocytes as a consequence of transgene expression. Hence, a link between desmosomal cadherins and beta-catenin stability and signaling was demonstrated, and it was shown that desmocollin cadherin expression can affect keratinocyte differentiation. Furthermore, the first function for a "b-type" desmocollin cadherin was demonstrated.

Alopecia↗

PubMed2004

Truncated mutants of the putative Wnt receptor LRP6/Arrow can stabilize beta-catenin independently of Frizzled proteins.

Secreted signaling proteins of the Wnt family are known to regulate a diverse range of developmental processes, and their signaling pathway through beta-catenin is frequently activated in cancer. The identification of both Frizzled and LRP5/6 (LRP: low-density lipoprotein receptor-related protein) proteins as components of cell-surface receptors for Wnt proteins has raised questions about their individual functions. We have investigated this issue through a structure-function analysis of Frizzled and LRP proteins that have been implicated in Wnt1 signaling. Consistent with other reports, we find that LRP6/Arrow proteins deleted for their extracellular domain are able to activate the Wnt/beta-catenin signaling pathway. Importantly, our results demonstrate that this signaling from LRP6/Arrow derivatives can occur in a Frizzled- and ligand-independent manner. Furthermore, we show that the PPSP motifs within the intracellular domain of LRP6 are required for signaling. In contrast to results with LRP6, overexpression of Frizzled proteins did not activate the pathway. Based on evidence of ligand binding to both Frizzled and LRP6, current models suggest that both proteins are components of a Wnt receptor complex that signals to beta-catenin. In light of these models, our data imply that LRP5/6/Arrow proteins constitute the distal signal-initiating component of these receptors. The results also support the notion that LRP5/6 are candidate oncogenes.

Animals↗

PubMed2003

Is there a role for Notch signalling in human breast cancer?

Aberrant Notch signalling has been observed in several human cancers, including acute T-cell lymphoblastic leukaemia and cervical cancer, and is strongly implicated in tumourigenesis. Unregulated Notch signalling in the mouse mammary gland leads to tumour formation. These results raise the possibility that Notch signalling might play a role in human breast cancer. There are currently few reports that address this question directly and this appears to be an area worthy of further investigation.

Breast Neoplasms↗

PubMed2002

Notching up another pathway.

The Notch proteins play a vital role in cell fate decisions in both invertebrate and vertebrate development. Careful analysis of this role has led to a model of signalling downstream of these receptors, via the CSL (CBF1, Suppressor of Hairless, Lag-1) family of transcription factors. There have been suggestions, however, that Notch can signal through other pathways. In the current paper, Ramain et al. provide compelling evidence for Notch signalling through a CSL-independent pathway and they demonstrate that the cytoplasmic protein, Deltex, is required for this signal. In addition, they show that Wnt signalling may regulate this Deltex-dependent signal.

Alleles↗

PubMed2002

CSL-independent Notch signalling: a checkpoint in cell fate decisions during development?

During development, signalling by members of the Notch family of cell surface receptors plays a widespread role in the assignation of cell fates within the process of lateral inhibition. This function of Notch is mediated by a well-established mechanism that relies on a ligand-induced release of the intracellular domain of Notch (NICD) and the interaction of this fragment with members of the CSL (CBF1, Suppressor of Hairless, Lag-1) family of transcription factors within the nucleus. However, there is increasing evidence that Notch can signal in CSL-independent modes.

Animals↗