Cell signalling by cytokine receptors

Question 1

what are cytokines?

Answer 1

a broad range of signalling molecules

Question 2

what are some examples of cytokines?

Answer 2

proteins, peptides, and glycoproteins
includes interferons and interleukins plus additional factors

Question 3

what are cytokines involved in?

Answer 3

Autocrine, paracrine and endocrine signalling

Question 4

what produces interleukins?

Answer 4

cells that have suffered damage

Question 5

how do cytokines act on cells?

Answer 5

cytokines act via cell surface cytokine receptors

Question 6

what is growth hormone?

Answer 6

peptide hormone (also called somatotropin) produced by somatotrophic cells in the anterior pituitary

Question 7

what signal increases the release of growth hormone?

Answer 7

GH-releasing hormone released from the hypothalamus
Ghrelin for the stomach

Question 8

what signal inhibits the release of growth hormone?

Answer 8

GH-inhibiting hormone (SS) also released from the hupothalamus

Question 9

where is growth hormone produced?

Answer 9

by the somatotrophic cells in the anterior pituitary

Question 10

what are the effects of growth hormone on the body?

Answer 10

Growth hormone has anabolic effects including muscle and bone growth
many Growth hormone actions are secondary to its ability to stimulate insulin-like growth factor 1 (IGF-1) release from the liver

Question 11

what is the process of growth hormone receptor signaling?

Answer 11

-Growth hormone binds to the growth hormone receptor on the surface of target cells, including the liver hepatocytes
- this causes two growth hormone receptors to come together and dimerize
- this dimerized receptor complex becomes active because the associated JAK2 proteins come into contact with each other
-JAK2 is a protein tyrosine kinase and when activated adds phosphates to intracellular signaling molecules including STAT5 and ERK1/2
-Phosphorylated STAT5 and ERK1/2 enter the nucleus and act as transcription factors turning on (or off) specific genes

Question 12

when does growth hormone receptor become active?

Answer 12

when growth hormone binds and the receptors dimerize
-the dimerized receptor becomes active because the associated JAK2 proteins come into contact with each other

Question 13

what is JAK2?

Answer 13

JAK2 is a protein tyrosine kinase

Question 14

what is the function of JAK2 once activated?

Answer 14

When activated JAK2 adds phosphates to intracellular signalling molecules including STAT5 and ERK1/2

Question 15

what is the role of phosphorylated STAT5 and ERK1/2?

Answer 15

enter the nucleus and act as transcription factors turning on (or off) specific genes

Question 16

what is the role of phosphorylated STAT5 and ERK1/2 in hepatocytes?

Answer 16

this would include increasing the production of IGF-1

Question 17

what are STATs?

Answer 17

Signal Transducers and Activators of Transcription

Question 18

what are the two forms of STAT5?

Answer 18

STAT5a and STAT5b which are very closely related

Question 19

what pathway is STAT5 involved in?

Answer 19

part of the GH signalling pathway

Question 20

what happens when STAT5 is phosphorylated?

Answer 20

When phosphorylated by JAK2 phospho-STAT5 (pSTAT5) may form homo or heterodimers

Question 21

what happens to pSTAT5 dimers?

Answer 21

once in the nucleus, the pSTAT5 dimers interact with transcription factor (GR) which is activated by glucocorticoids to turn on specific genes

Question 22

what happens when pSTAT5 enters the nucleus?

Answer 22

pSTAT5 dimers interact with a transcription factor which is activated by glucocorticoids to turn on specific genes

Question 23

what activates transcription factor in the JAK/STAT pathway?

Answer 23

activated by glucocorticoids

Question 24

what turns off the pSTAT5 response?

Answer 24

intracellular negative feedback pathways

Question 25

how do STAT5 dimers enter the nucleus?

Answer 25

through the nuclear pore