Biology subjects

Harris, M. T.

Publications and source records attributed to Harris, M. T..

2 recordsLinked to original sources

bioRxiv2022

The Insulin receptor and Insulin like growth factor receptor 5 UTRs support translation initiation independently of eIF4G1

Protein synthesis is tightly regulated under stress conditions where energy may be scarce. Despite global repression of translation, some transcripts remain actively translated in order for the cell to be able to respond to the insult or prepare to quickly return normal cellular function after the stress ends. For the insulin receptor (Insr) and insulin-like growth factor receptor (Igf1r) transcripts this translation is mediated by an internal ribosome entry site (IRES) in their 5UTRs that functions independently of eukaryotic initiation factor 4A (eIF4A) and eIF4E. Here we show that these cellular IRESes are also able to promote translation independently of the scaffolding protein eIF4G1 both in vitro and in the cell. BackgroundIRES mediated translation initiation requires a different repertoire of factors than canonical cap-dependent translation. ResultsTreatments that inhibit the canonical translation factor eIF4G1 have little or no effect on the ability of the Insr and Igf1r cellular IRESes to promote translation. ConclusionTranscripts for two cellular receptors contain RNA elements that facilitate translation initiation without intact eIF4G1 SignificanceCellular IRES mechanisms may resemble viral type III IRESes allowing them to promote translate with a limited number of initiation factors allowing them to work under stress conditions when canonical translation is repressed.

molecular biology↗

bioRxiv2018

Reinterpretation of the localization of the ATP binding cassette transporter ABCG1 in insulin-secreting cells and insights regarding its trafficking and function

The ABC transporter ABCG1 regulates intracellular cholesterol. We showed previously that ABCG1 deficiency inhibits insulin secretion by pancreatic beta cells and, based on its immunolocalization to insulin granules, proposed its essential role in forming cholesterol-enriched granule membranes. While we confirm elsewhere that ABCG1, alongside ABCA1 and oxysterol binding protein OSBP, supports insulin granule formation, the aim here is to update our localization and to provide added insight regarding ABCG1s trafficking and sites of function. We show that stably expressed GFP-tagged ABCG1 closely mimics the distribution of endogenous ABCG1 in pancreatic INS1 cells and accumulates in the trans-Golgi network (TGN), endosomal recycling compartment (ERC) and on the cell surface but not on insulin granules, early or late endosomes. Notably, ABCG1 is short-lived, and proteasomal and lysosomal inhibitors both decrease its degradation. Following blockade of protein synthesis, GFP-ABCG1 first disappears from the ER and TGN and later from the ERC and plasma membrane. Beyond aiding granule formation, our findings raise the prospect that ABCG1 may act beyond the TGN to regulate activities involving the endocytic pathway, especially as the amount of transferrin receptor is increased in ABCGI-deficient cells. Thus, ABCG1 may function at multiple intracellular sites and the plasma membrane as a roving sensor and modulator of cholesterol distribution and membrane trafficking.

cell biology↗