Lecture 9 - Immediate Early Genes

Question 1

Immediate Early Genes:

Answer 1

• Their transcription is induced quickly after stimulation (<1h)
• Do not require the synthesis of new proteins for their transcription
• Can encode for proteins with different functions (Transcription Factors, enzymes, cytokines, growth factors)
• Controlled by the phosphorylation and activation of transcription factors that act on their promoters

Question 2

Secondary Response Genes:

Answer 2

• Transcription is Delayed

- May require the synthesis of new proteins for their transcription

Question 3

Control of Transcription Factors by Phosphorylation:

Answer 3

Phosphorylation promotes cytoplasmic location:

• Foxo transcription factors:
• Akt phosphorylates Foxo -> Enabling 14-3-3 binding

Phosphorylation promotes nuclear location:

• STAT transcription factors:
• JAK phosphorylates STATs -> Enabling dimerisation and translocation to nucleus

Question 4

CREB:

Answer 4

• Member of the bZip family of transcription factors (bZip domains are DNA binding domains)
• In addition to the bZip domain, CREB contains Q1, KID, and Q2 domains (Q = Glutamine Rich Domains, KID - Kinase Induced Domains)
• Binds to CRE (cAMP response elements) sequences in the promoters of immediate early genes
• Roles in development, metabolism, synaptic activity, and innate immunity
• PKA phosphorylates CREB on Ser133 (and cAMP activates PKA)
• CBP and p300 are 2 related transcription co-activators, they are large proteins with multiple domains, including Histone Acetyl Transferase (HAT)
• CBP and p300 are recruited due to phosphorylation of CREB at Ser133 by PKA
• The KID domain of CREB interacts with the KIX domain of CBP or p300
• —The unphosphorylated CREB KID domain has a disordered structure, phosphorylation of Ser133 stabilises the structure
• —Interaction of KID and KIX domains is then enabled, further stabilising the structure
• Once recruited to CREB, CBP or p300 acetylate histones, leading to increased transcription
• CREB can also be phoshphorylated downstream of other signalling pathways apart from PKA, including Ca2+ and MAPK signalling

Question 5

CRTCs:

Answer 5

CRTC = CREB Regulated Transcription Co-Activator

Question 6

CRTCs:

Answer 6

CRTC = CREB Regulated Transcription Co-Activator:
-3 isoforms: CRTC1, 2, 3

• No known catalytic activity
• N-terminal region binds to CREBs bZip domain (does not need CREB to be phosphorylated at Ser133)
• Act to stabilise the interaction between CREB and CBP or between CREB and components of the RNA polymerase complex
• PKA controls nuclear localisation of CRTCs via phosphorylation (phosphorylation at 3 key sites in CRTCs enable 14-3-3 binding, masking a nuclear localisation sequence, therefore CRTC remains in cytoplasm. Dephosphorylation allows CRTCs to translocate to the nucleus where it can bind CRE)
• CRTCS are phosphorylated by SIKs

PKA phosphorylates SIKs and inhibits their ability to phosphorylate CRTCs