{"type": "root", "children": [{"type": "p", "children": [{"type": "t", "text": "\nThe studies reveal that Rlf functions as a critical mediator linking Ras activation to transcriptional responses in cardiac cells. In neonatal rat ventricular myocytes as well as in transgenic mouse models, activated Ras induces myocardial cell growth and cardiac hypertrophy marker expression through pathways that involve Rlf. Rlf promotes transcription of genes such as atrial natriuretic factor and myosin light chain‐2 by activating promoter elements—specifically through the proximal serum response element—and requires the activity of Ral and Cdc42. Moreover, Rlf enhances alpha₁-adrenergic receptor–induced responses, suggesting it plays a selective role in modulating hypertrophic signaling without causing a global transcriptional increase."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "1"}]}, {"type": "t", "text": "\n"}]}, {"type": "t", "text": "\n\n"}, {"type": "p", "children": [{"type": "t", "text": "\nStructural insights further define Rlf as a guanine nucleotide exchange factor for the small G-proteins RalA and RalB, effectively coupling Ras to Ral-signaling. The crystal structure of its catalytic module, comprising both REM- and CDC25-homology domains, is characterized by an extended, three-stranded β-sheet—termed the flagpole—that stabilizes the REM-domain’s orientation relative to the CDC25 domain. A unique proline-rich sequence in this flagpole region mediates specific interactions with SH3 domains, thereby contributing to the selective recruitment of signaling partners."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "2"}]}, {"type": "t", "text": "\n"}]}, {"type": "t", "text": "\n\n"}, {"type": "p", "children": [{"type": "t", "text": "\nIn summary, Rlf emerges as a vital, previously unrecognized effector in myocardial signaling that not only transduces signals from activated Ras to Ral GTPases but also orchestrates specific transcriptional programs linked to cardiac hypertrophy. The mechanistic details—from both functional studies in cardiomyocytes and structural characterizations—underscore its role in fine-tuning cellular responses to hypertrophic stimuli."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "1"}]}, {"type": "t", "text": "\n"}]}, {"type": "rg", "children": [{"type": "r", "ref": 1, "children": [{"type": "t", "text": "Ginell R Post, Carol Swiderski, Bruce A Waldrop, et al. "}, {"type": "b", "children": [{"type": "t", "text": "Guanine nucleotide exchange factor-like factor (Rlf) induces gene expression and potentiates alpha 1-adrenergic receptor-induced transcriptional responses in neonatal rat ventricular myocytes."}]}, {"type": "t", "text": " "}, {"type": "i", "children": [{"type": "t", "text": "J Biol Chem (2002)"}]}, {"type": "t", "text": " DOI: "}, {"type": "a", "children": [{"type": "t", "text": "10.1074/jbc.M111844200"}], "href": "https://doi.org/10.1074/jbc.M111844200"}, {"type": "t", "text": " PMID: "}, {"type": "a", "children": [{"type": "t", "text": "11847222"}], "href": "https://pubmed.ncbi.nlm.nih.gov/11847222"}]}, {"type": "r", "ref": 2, "children": [{"type": "t", "text": "Milica Popovic, Arjen J Jakobi, Marije Rensen-de Leeuw, et al. "}, {"type": "b", "children": [{"type": "t", "text": "The guanine nucleotide exchange factor Rlf interacts with SH3 domain-containing proteins via a binding site with a preselected conformation."}]}, {"type": "t", "text": " "}, {"type": "i", "children": [{"type": "t", "text": "J Struct Biol (2013)"}]}, {"type": "t", "text": " DOI: "}, {"type": "a", "children": [{"type": "t", "text": "10.1016/j.jsb.2013.07.009"}], "href": "https://doi.org/10.1016/j.jsb.2013.07.009"}, {"type": "t", "text": " PMID: "}, {"type": "a", "children": [{"type": "t", "text": "23891840"}], "href": "https://pubmed.ncbi.nlm.nih.gov/23891840"}]}]}]}