Transcription factor that can activate or repress transcription in response to physiological and pathological stimuli. Binds with high affinity to GC-rich motifs and regulates the expression of a large number of genes involved in a variety of processes such as cell growth, apoptosis, differentiation and immune responses. Highly regulated by post-translational modifications (phosphorylations, sumoylation, proteolytic cleavage, glycosylation and acetylation). Binds also the PDGFR-alpha G-box promoter. May have a role in modulating the cellular response to DNA damage. Implicated in chromatin remodeling. Plays a role in the recruitment of SMARCA4/BRG1 on the c-FOS promoter Plays an essential role in the regulation of FE65 gene expression (By similarity). Positively regulates the transcription of the core clock component ARNTL/BMAL1 (PubMed:24030830). Plays a role in protecting cells against oxidative stress following brain injury by regulating the expression of RNF112 (PubMed:27918959). Interacts with ATF7IP, ATF7IP2, BAHD1, POGZ, HCFC1, AATF and PHC2. Interacts with SV40 VP2/3 proteins. Interacts with SV40 major capsid protein VP1; this interaction leads to a cooperativity between the 2 proteins in DNA binding. Interacts with HLTF; the interaction may be required for basal transcriptional activity of HLTF. Interacts (deacetylated form) with EP300; the interaction enhances gene expression. Interacts with HDAC1 and JUN. Interacts with ELF1; the interaction is inhibited by glycosylation of SP1. Interaction with NFYA; the interaction is inhibited by glycosylation of SP1. Interacts with SMARCA4/BRG1. Interacts with ATF7IP and TBP. Interacts with MEIS2 isoform 4 and PBX1 isoform PBX1a. Interacts with EGR1 (By similarity). Interacts with RNF112 in an oxidative stress-regulated manner (PubMed:27918959). Interacts with ZBTB7A; ZBTB7A prevents the binding to GC-rich motifs in promoters and represses the transcriptional activity of SP1 (By similarity). Interacts with DDX3X; this interaction potentiates SP1-induced CDKN1A/WAF1/CIP1 transcription (By similarity). (Microbial infection) Interacts with murine minute virus NS1; this interaction allows high levels of viral P38 promoter transactivation by NS1. Nuclear location is governed by glycosylated/phosphorylated states. Insulin promotes nuclear location, while glucagon favors cytoplasmic location (By similarity). Up-regulated by traumatic brain injury and hydrogen peroxide (at protein level)(PubMed:27918959). The 9aaTAD motif is a transactivation domain present in a large number of yeast and animal transcription factors. Phosphorylated on multiple serine and threonine residues. Phosphorylation is coupled to ubiquitination, sumoylation and proteolytic processing. Phosphorylation on Ser-61 enhances proteolytic cleavage. Phosphorylation on Ser-7 enhances ubiquitination and protein degradation. Hyperphosphorylation on Ser-103 in response to DNA damage has no effect on transcriptional activity. MAPK1/MAPK3-mediated phosphorylation on Thr-455 and Thr-738 enhances VEGF transcription but, represses FGF2-triggered PDGFR-alpha transcription. Also implicated in the repression of RECK by ERBB2. Hyperphosphorylated on Thr-280 and Thr-738 during mitosis by MAPK8 shielding SP1 from degradation by the ubiquitin-dependent pathway. Phosphorylated in the zinc-finger domain by calmodulin-activated PKCzeta. Phosphorylation on Ser-642 by PKCzeta is critical for TSA-activated LHR gene expression through release of its repressor, p107. Phosphorylation on Thr-669, Ser-671 and Thr-682 is stimulated by angiotensin II via the AT1 receptor inducing increased binding to the PDGF-D promoter. This phosphorylation is increased in injured artey wall. Ser-61 and Thr-682 can both be dephosphorylated by PP2A during cell-cycle interphase. Dephosphorylation on Ser-61 leads to increased chromatin association during interphase and increases the transcriptional activity. On insulin stimulation, sequentially glycosylated and phosphorylated on several C-terminal serine and threonine residues (By similarity). Acetylated. Acetylation/deacetylation events affect transcriptional activity. Deacetylation leads to an increase in the expression the 12(s)-lipooxygenase gene though recruitment of p300 to the promoter (By similarity). Ubiquitinated. Ubiquitination occurs on the C-terminal proteolytically-cleaved peptide and is triggered by phosphorylation (By similarity). Sumoylated with SUMO1. Sumoylation modulates proteolytic cleavage of the N-terminal repressor domain. Sumoylation levels are attenuated during tumorigenesis. Phosphorylation mediates SP1 desumoylation (By similarity). Proteolytic cleavage in the N-terminal repressor domain is prevented by sumoylation. The C-terminal cleaved product is susceptible to degradation (By similarity). O-glycosylated; Contains 8 N-acetylglucosamine side chains. Levels are controlled by insulin and the SP1 phosphorylation states. Insulin-mediated O-glycosylation locates SP1 to the nucleus, where it is sequentially deglycosylated and phosphorylated. O-glycosylation affects transcriptional activity through disrupting the interaction with a number of transcription factors including ELF1 and NFYA. Inhibited by peroxisomome proliferator receptor gamma (PPARgamma) (By similarity). Belongs to the Sp1 C2H2-type zinc-finger protein family.