BioPAX pathway converted from "LKB1 forms a trimeric complex with STRAD and MO25" in the Reactome database.LKB1 forms a trimeric complex with STRAD and MO25LKB1 forms a trimeric complex with STRAD and MO25Upon complex formation with STRAD and MO25, LKB1 (also known as serine/threonine kinase 11, STK11) is mostly cytosolic. LKB1 attains 20x activity towards the substrates belonging to the subfamily of AMPK-like kinases (5'AMP-activated protein kinases).Authored: Katajisto, P, Makela, T, Wu, J, 2008-11-19Reviewed: Zwartkruis, Fried J T, 2015-05-14Edited: Jassal, B, 2008-11-19 15:14:38Reactome DB_ID: 3809541cytosolGO0005829UniProt:Q15831 STK11STK11STK11PJSLKB1FUNCTION Tumor suppressor serine/threonine-protein kinase that controls the activity of AMP-activated protein kinase (AMPK) family members, thereby playing a role in various processes such as cell metabolism, cell polarity, apoptosis and DNA damage response. Acts by phosphorylating the T-loop of AMPK family proteins, thus promoting their activity: phosphorylates PRKAA1, PRKAA2, BRSK1, BRSK2, MARK1, MARK2, MARK3, MARK4, NUAK1, NUAK2, SIK1, SIK2, SIK3 and SNRK but not MELK. Also phosphorylates non-AMPK family proteins such as STRADA, PTEN and possibly p53/TP53. Acts as a key upstream regulator of AMPK by mediating phosphorylation and activation of AMPK catalytic subunits PRKAA1 and PRKAA2 and thereby regulates processes including: inhibition of signaling pathways that promote cell growth and proliferation when energy levels are low, glucose homeostasis in liver, activation of autophagy when cells undergo nutrient deprivation, and B-cell differentiation in the germinal center in response to DNA damage. Also acts as a regulator of cellular polarity by remodeling the actin cytoskeleton. Required for cortical neuron polarization by mediating phosphorylation and activation of BRSK1 and BRSK2, leading to axon initiation and specification. Involved in DNA damage response: interacts with p53/TP53 and recruited to the CDKN1A/WAF1 promoter to participate in transcription activation. Able to phosphorylate p53/TP53; the relevance of such result in vivo is however unclear and phosphorylation may be indirect and mediated by downstream STK11/LKB1 kinase NUAK1. Also acts as a mediator of p53/TP53-dependent apoptosis via interaction with p53/TP53: translocates to the mitochondrion during apoptosis and regulates p53/TP53-dependent apoptosis pathways. In vein endothelial cells, inhibits PI3K/Akt signaling activity and thus induces apoptosis in response to the oxidant peroxynitrite (in vitro). Regulates UV radiation-induced DNA damage response mediated by CDKN1A. In association with NUAK1, phosphorylates CDKN1A in response to UV radiation and contributes to its degradation which is necessary for optimal DNA repair (PubMed:25329316).ACTIVITY REGULATION Activated by forming a complex with STRAD (STRADA or STRADB) and CAB39/MO25 (CAB39/MO25alpha or CAB39L/MO25beta): STRADA (or STRADB)-binding promotes a conformational change of STK11/LKB1 in an active conformation, which is stabilized by CAB39/MO25alpha (or CAB39L/MO25beta) interacting with the STK11/LKB1 activation loop. Sequestration in the nucleus by NR4A1 prevents it from phosphorylating and activating cytoplasmic AMPK.SUBUNIT Catalytic component of a trimeric complex composed of STK11/LKB1, STRAD (STRADA or STRADB) and CAB39/MO25 (CAB39/MO25alpha or CAB39L/MO25beta): the complex tethers STK11/LKB1 in the cytoplasm and stimulates its catalytic activity. Found in a ternary complex composed of SMAD4, STK11/LKB1 and STK11IP. Interacts with p53/TP53, SMAD4, STK11IP and WDR6. Interacts with NR4A1. Interacts with NISCH; this interaction may increase STK11 activity. Interacts with PTEN; leading to PTEN phosphorylation. Interacts with SIRT1; the interaction deacetylates STK11. Interacts with CDKN1A.TISSUE SPECIFICITY Ubiquitously expressed. Strongest expression in testis and fetal liver.PTM Phosphorylated by ATM at Thr-363 following ionizing radiation (IR). Phosphorylation at Ser-428 by RPS6KA1 and/or some PKA is required to inhibit cell growth. Phosphorylation at Ser-428 is also required during neuronal polarization to mediate phosphorylation of BRSK1 and BRSK2 (By similarity). Phosphorylation by PKC/PRKCZ at Ser-428 promotes peroxynitrite-induced nuclear export of STK11, leading to PTEN activation and subsequent inhibition of AKT signaling. Phosphorylation by PKC/PRKCZ at Ser-399 in isoform 2 promotes metformin (or peroxynitrite)-induced nuclear export of STK11 and activation of AMPK. UV radiation-induced phosphorylation at Thr-363 mediates CDKN1A degradation (By similarity).PTM Acetylated. Deacetylation at Lys-48 enhances cytoplasmic localization and kinase activity in vitro.DISEASE Defects in STK11 are associated with some sporadic cancers, especially lung cancers. Frequently mutated and inactivated in non-small cell lung cancer (NSCLC). Defects promote lung cancerigenesis process, especially lung cancer progression and metastasis. Confers lung adenocarcinoma the ability to trans-differentiate into squamous cell carcinoma. Also able to promotes lung cancer metastasis, via both cancer-cell autonomous and non-cancer-cell autonomous mechanisms.SIMILARITY Belongs to the protein kinase superfamily. CAMK Ser/Thr protein kinase family. LKB1 subfamily.Reactomehttp://www.reactome.orgHomo sapiensNCBI Taxonomy9606UniProtQ15831Chain Coordinates1EQUAL430EQUALConverted from EntitySet in ReactomeReactome DB_ID: 3809751MO25 [cytosol]Converted from EntitySet in Reactome. Each synonym is a name of a PhysicalEntity, and each XREF points to one PhysicalEntityCAB39 [cytosol]CAB39L [cytosol]UniProtQ9Y376UniProtQ9H9S4Converted from EntitySet in ReactomeReactome DB_ID: 3809631STRAD [cytosol]Converted from EntitySet in Reactome. Each synonym is a name of a PhysicalEntity, and each XREF points to one PhysicalEntitySTRADB [cytosol]STRADA [cytosol]UniProtQ9C0K7UniProtQ7RTN6Reactome DB_ID: 3809671LKB1:STRAD:MO25 [cytosol]LKB1:STRAD:MO25STK11:MO25:STRADReactome DB_ID: 38095411EQUAL430EQUALConverted from EntitySet in ReactomeReactome DB_ID: 3809751Converted from EntitySet in ReactomeReactome DB_ID: 3809631Reactome Database ID Release 75380967Database identifier. Use this URL to connect to the web page of this instance in Reactome: http://www.reactome.org/cgi-bin/eventbrowser?DB=gk_current&ID=380967ReactomeR-HSA-3809671Reactome stable identifier. Use this URL to connect to the web page of this instance in Reactome: http://www.reactome.org/cgi-bin/eventbrowser_st_id?ST_ID=R-HSA-380967.1Reactome Database ID Release 75380942Database identifier. Use this URL to connect to the web page of this instance in Reactome: http://www.reactome.org/cgi-bin/eventbrowser?DB=gk_current&ID=380942ReactomeR-HSA-3809421Reactome stable identifier. Use this URL to connect to the web page of this instance in Reactome: http://www.reactome.org/cgi-bin/eventbrowser_st_id?ST_ID=R-HSA-380942.114517248Pubmed2003MO25alpha/beta interact with STRADalpha/beta enhancing their ability to bind, activate and localize LKB1 in the cytoplasmBoudeau, JBaas, AFDeak, MMorrice, NAKieloch, ASchutkowski, MPrescott, ARClevers, Hans CAlessi, DREMBO J 22:5102-1412805220Pubmed2003Activation of the tumour suppressor kinase LKB1 by the STE20-like pseudokinase STRADBaas, AFBoudeau, JSapkota, GPSmit, LMedema, RMorrice, NAAlessi, DRClevers, Hans CEMBO J 22:3062-72