Biomedical subjects

Simone E Salghetti

Publications and source records attributed to Simone E Salghetti.

5 recordsLinked to original sources

PubMed2005

A conserved element in Myc that negatively regulates its proapoptotic activity.

Myc is an oncoprotein transcription factor that promotes cell proliferation and apoptosis. Analysis of highly conserved elements within vertebrate Myc proteins has been instrumental in defining the functions of the Myc protein. Here, we probe the role of a highly conserved, but little studied, element within the central region of c-Myc, termed 'Myc box III' (MbIII). We show that MbIII is important for transcriptional repression by Myc, and for transformation both in vitro and in a mouse model of lymphomagenesis. Curiously, disruption of MbIII decreases transformation activity by increasing the efficiency with which Myc can induce apoptosis, suggesting that MbIII is a negative regulator of programmed cell death. These findings reveal a role for MbIII in Myc biology, and establish that the oncogenic capacity of Myc is linked directly to its ability to temper the apoptotic response.

Animals↗

PubMed2004

Multiple cell-type-specific elements regulate Myc protein stability.

Myc is a highly unstable transcription factor that is destroyed by ubiquitin (Ub)-mediated proteolysis. We have previously identified an amino-terminal 'degron' within Myc that signals its destruction; this degron spans the transcriptional activation domain of Myc, and includes two highly conserved regions called Myc boxes I and II. We now report the identification of a second element--the D-element--which is also required for Myc proteolysis. The centrally located D-element is distinct from the PEST domain in Myc, but includes Myc box III, a third highly conserved region with no previously known function. We show that deletion of the D-element stabilizes the Myc protein without affecting its ubiquitylation, and report that the D-element and the degron act in a cell-type-specific manner to direct Myc proteolysis. These data thus demonstrate that Myc stability is regulated at both the ubiquitylation and postubiquitylation levels, and reveal that substrates of the Ub-proteasome system can be targeted for destruction differently in different cell types.

Amino Acid Sequence↗

PubMed2004

From silencing to gene expression: real-time analysis in single cells.

We have developed an inducible system to visualize gene expression at the levels of DNA, RNA and protein in living cells. The system is composed of a 200 copy transgene array integrated into a euchromatic region of chromosome 1 in human U2OS cells. The condensed array is heterochromatic as it is associated with HP1, histone H3 methylated at lysine 9, and several histone methyltransferases. Upon transcriptional induction, HP1alpha is depleted from the locus and the histone variant H3.3 is deposited suggesting that histone exchange is a mechanism through which heterochromatin is transformed into a transcriptionally active state. RNA levels at the transcription site increase immediately after the induction of transcription and the rate of synthesis slows over time. Using this system, we are able to correlate changes in chromatin structure with the progression of transcriptional activation allowing us to obtain a real-time integrative view of gene expression.

Animals↗

PubMed2003

Skp2 regulates Myc protein stability and activity.

Myc is an oncoprotein transcription factor that plays a prominent role in cancer. Like many transcription factors, Myc is an unstable protein that is destroyed by ubiquitin (Ub)-mediated proteolysis. Here, we report that the oncoprotein and Ub ligase Skp2 regulates Myc ubiquitylation and stability. Because of the growing number of Ub ligases that function as transcriptional coactivators, we speculated that Skp2 might also regulate Myc's transcriptional activity. Consistent with this model, we also show that Skp2 is a transcriptional coactivator for Myc, recognizing an essential element within the Myc activation domain and activating Myc target genes. These data suggest that Skp2 functions to connect Myc activity and destruction, and reveal an unexpected oncoprotein connection that may play an important role in controlling cell growth in normal and cancer cells.

Animals↗

PubMed2002

Stable and unstable pools of Myc protein exist in human cells.

The oncoprotein transcription factor Myc plays a crucial role in the control of cell growth and proliferation. Consistent with its potent growth-promoting properties, cells have evolved a number of mechanisms to limit the activity and accumulation of the Myc protein. One of the most striking of these mechanisms is ubiquitin (Ub)-mediated proteolysis, which typically destroys Myc within minutes of its synthesis. Here we show that, despite the extreme instability of the Myc protein, cells contain a pool of Myc that is metabolically stable. Entry of Myc into the stable pool is signaled by an element within the carboxy-terminus of the protein, and is a cell-specific process that is regulated during mitosis and by interaction with Max. These data demonstrate that - even for a rapidly turned-over protein such as Myc - metabolically stable and unstable forms of a protein can co-exist in cells, and suggest that the rate of destruction of Myc molecules is linked to their specific functions.

Cell Cycle↗