WBR0733

Author	[[PageAuthor::Yazan Daaboul, M.D. (Reviewed by Yazan Daaboul, M.D.)]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Physiology
Sub Category	SubCategory::Endocrine
Prompt	[[Prompt::A researcher is studying the signaling pathways of hormones and their corresponding mechanisms of achieving their regulatory functions. Using mice, he activates liver fat-storing cells (FSCs) using phorbol myristate acetate to increase levels of platelet-derived growth factor (PDGF). In vitro experiments demonstrate that profiling of an enzyme activity is significantly increased following the increased production of PDGF. Which other endogenous compound will most likely have the same signaling effect as PDGF?]]
Answer A	AnswerA::Insulin
Answer A Explanation	AnswerAExp::Insulin, like PDGF, uses the intrinsic tyrosine kinase activity to achieve its hormonal effects.
Answer B	AnswerB::Follicle-stimulating hormone (FSH)
Answer B Explanation	AnswerBExp::FSH uses the cAMP pathway to achieve its hormonal effect.
Answer C	AnswerC::Oxytocin
Answer C Explanation	AnswerCExp::Oxytocin uses the inositol triphosphate (IP3) signaling pathway to achieve its hormonal effects.
Answer D	AnswerD::Prolactin
Answer D Explanation	AnswerDExp::Prolactin uses a receptor-associated tyrosine kinase pathway to achieve its hormonal effect.
Answer E	AnswerE::Cortisol
Answer E Explanation	AnswerEExp::Cortisol utilizes a specific steroid receptor to achieve its hormonal effects.
Right Answer	RightAnswer::A
Explanation	[[Explanation::Platelet-derived growth factor (PDGF) is a compound found in platelet alpha-granules and other numerous cell types. It exerts its effects via an autocrine or paracrine fashion. PDGF helps growth and proliferation of smooth muscle cells and fibroblasts. It has been hypothesized that PDGF's proliferative function may contribute to proliferative pathological processes, such as cancers and atherosclerosis. PDGF, similar to other growth factors and insulin, achieves its hormonal effects by the intrinsic tyrosine kinase signaling pathway. PDGF contains extracellular ligang-binding domains that are associated with intracellular domains. Following ligand binding, the receptor dimerizes, with each subunit binding to one receptor molecule. Dimerization then causes activation of the enzyme protein kinase on the receptor via phosphorylation mechanisms. Educational Objective: Growth factors, such as PDGF, and insulin achieve their hormonal activity by the intrinsic tyrosine kinase signaling pathway. References: Heldin CH, Westermark B. Platelet-derived growth factor: mechanism of action and possible in vivo function. Cell Regulation. 1990;1:555-566. First Aid 2014 page 315]]
Approved	Approved::Yes
Keyword	WBRKeyword::PDGF, WBRKeyword::Platelet, WBRKeyword::Growth, WBRKeyword::Factor, WBRKeyword::Insulin, WBRKeyword::Intrinsic, WBRKeyword::Tyrosine, WBRKeyword::Kinase, WBRKeyword::Pathway, WBRKeyword::Signaling, WBRKeyword::Hormone, WBRKeyword::Platelet derived growth factor, WBRKeyword::Intrinsic tyrosine kinase, WBRKeyword::Intrinsic tyrosine kinase pathway
Linked Question	Linked::
Order in Linked Questions	LinkedOrder::