KLF1 explained

Krueppel-like factor 1 is a protein that in humans is encoded by the KLF1 gene. The gene for KLF1 is on the human chromosome 19 and on mouse chromosome 8. Krueppel-like factor 1 is a transcription factor that is necessary for the proper maturation of erythroid (red blood) cells.

Structure

The molecule has two domains; the transactivation domain and the chromatin-remodeling domain. The carboxyl (C) terminal is composed of three C2H2 zinc fingers that binds to DNA, and the amino (N) terminus is proline rich and acidic.[1]

Function

Studies in mice first demonstrated the critical function of KLF1 in hematopoietic development. KLF1 deficient (knockout) mouse embryos exhibit a lethal anemic phenotype, fail to promote the transcription of adult β-globin, and die by embryonic day 15.[2] Over-expression of KLF1 results in a reduction of the number of circulating platelets and hastens the onset of the β-globin gene.[3]

KLF1 coordinates the regulation of six cellular pathways that are all essential to terminal erythroid differentiation:[4]

  1. Cell Membrane & Cytoskeleton
  2. Apoptosis
  3. Heme Synthesis & Transport
  4. Cell Cycling
  5. Iron Procurement
  6. Globin Chain Production

It has also been linked to three main processes that are all essential to transcription of the β globin gene:

  1. Chromatin remodeling
  2. Modulation of the gamma to beta globin switch
  3. Transcriptional activation

KLF1 binds specifically to the "CACCC" motif of the β-globin gene promoter. When natural mutations occur in the promoter, β+ thalassemia can arise in humans. Thalassemia's prevalence (2 million worldwide carry the trait) makes KLF1 clinically significant.

Clinical significance

Next-Generation sequencing efforts have revealed a surprisingly high prevalence of mutations in human KLF1.[5] The chance of a KLF1 null child being conceived is approximately 1:24,000 in Southern China.[6] With pre-natal blood transfusions and bone marrow transplant, it is possible to be born without KLF1.[7] Most mutations in KLF1 lead to a recessive loss-of-function phenotype, however semi-dominant mutations have been identified in humans[8] and mice[9] as the cause of a rare inherited anemia CDA type IV. Additional family studies and clinical research[10] unveiled the molecular genetics of the HPFH KLF1-related condition and established KLF1 as a novel quantitative trait locus for HbF (HBFQTL6). Permissive nature of the role of KLF1 on expression of several RBC antigens are evidenced by a series of known KLF1 mutations which are named after its modifier gene effect on Lutheral blood group In(Lu) ie "Inhibitor of Lutheran". Interestingly no homozygouse alive human examples are known, corroborating with the Embryonic lethality of KLF1 homozygous mice. So the In(Lu) mutatants are significantly heteroinsuffient for KLF1 function such that RBC are formed, but there is an apparent dominant negative effect on expression of Lutheran Antigen (Basal cell adhesion Molecule) after which it was named, but also significant but somewhat variable degree of inhibition of expression of Colton (Aquaporin1), Ok (CD147 ie EMMPRIN), Indian(CD44), Duffy (Duffy antigen/chemokine receptor or Fy), Scianna (ERMAP), MN (glycophorin A), Diego(band 3), P1, i, AnWj (CD44) etc. Antigens on RBC membrane,[11] and some of which might overlap with KLF1 mutations causing the fraction of hereditary persistence of fetal hemoglobin with CDA type IV.

Notes and References

  1. Brown RC, Pattison S, van Ree J, Coghill E, Perkins A, Jane SM, Cunningham JM . Distinct domains of erythroid Krüppel-like factor modulate chromatin remodeling and transactivation at the endogenous beta-globin gene promoter . Molecular and Cellular Biology . 22 . 1 . 161–70 . January 2002 . 11739731 . 134232 . 10.1128/mcb.22.1.161-170.2002 .
  2. Perkins AC, Sharpe AH, Orkin SH . Lethal beta-thalassaemia in mice lacking the erythroid CACCC-transcription factor EKLF . Nature . 375 . 6529 . 318–22 . May 1995 . 7753195 . 10.1038/375318a0 . 1995Natur.375..318P . 4300395 .
  3. Tewari R, Gillemans N, Wijgerde M, Nuez B, von Lindern M, Grosveld F, Philipsen S . Erythroid Krüppel-like factor (EKLF) is active in primitive and definitive erythroid cells and is required for the function of 5'HS3 of the beta-globin locus control region . The EMBO Journal . 17 . 8 . 2334–41 . April 1998 . 9545245 . 1170576 . 10.1093/emboj/17.8.2334 .
  4. Tallack MR, Perkins AC . KLF1 directly coordinates almost all aspects of terminal erythroid differentiation . IUBMB Life . 62 . 12 . 886–90 . December 2010 . 21190291 . 10.1002/iub.404 . 10762358 .
  5. Gillinder K, Magor G, Perkins A . Variable serologic and other phenotypes due to KLF1 mutations . Transfusion . 58 . 5 . 1324–1325 . May 2018 . 29683509 . 10.1111/trf.14529 . 5062082 .
  6. Perkins A, Xu X, Higgs DR, Patrinos GP, Arnaud L, Bieker JJ, Philipsen S . Krüppeling erythropoiesis: an unexpected broad spectrum of human red blood cell disorders due to KLF1 variants . Blood . 127 . 15 . 1856–62 . April 2016 . 26903544 . 4832505 . 10.1182/blood-2016-01-694331 . Sjaak . George . Lionel . James .
  7. Magor GW, Tallack MR, Gillinder KR, Bell CC, McCallum N, Williams B, Perkins AC . KLF1-null neonates display hydrops fetalis and a deranged erythroid transcriptome . Blood . 125 . 15 . 2405–17 . April 2015 . 25724378 . 4521397 . 10.1182/blood-2014-08-590968 .
  8. Arnaud L, Saison C, Helias V, Lucien N, Steschenko D, Giarratana MC, Prehu C, Foliguet B, Montout L, de Brevern AG, Francina A, Ripoche P, Fenneteau O, Da Costa L, Peyrard T, Coghlan G, Illum N, Birgens H, Tamary H, Iolascon A, Delaunay J, Tchernia G, Cartron JP . A dominant mutation in the gene encoding the erythroid transcription factor KLF1 causes a congenital dyserythropoietic anemia . American Journal of Human Genetics . 87 . 5 . 721–7 . November 2010 . 21055716 . 2978953 . 10.1016/j.ajhg.2010.10.010 .
  9. Gillinder KR, Ilsley MD, Nébor D, Sachidanandam R, Lajoie M, Magor GW, Tallack MR, Bailey T, Landsberg MJ, Mackay JP, Parker MW, Miles LA, Graber JH, Peters LL, Bieker JJ, Perkins AC . Promiscuous DNA-binding of a mutant zinc finger protein corrupts the transcriptome and diminishes cell viability . Nucleic Acids Research . 45 . 3 . 1130–1143 . February 2017 . 28180284 . 5388391 . 10.1093/nar/gkw1014 .
  10. Borg J, Papadopoulos P, Georgitsi M, Gutiérrez L, Grech G, Fanis P, Phylactides M, Verkerk AJ, van der Spek PJ, Scerri CA, Cassar W, Galdies R, van Ijcken W, Ozgür Z, Gillemans N, Hou J, Bugeja M, Grosveld FG, von Lindern M, Felice AE, Patrinos GP, Philipsen S . Haploinsufficiency for the erythroid transcription factor KLF1 causes hereditary persistence of fetal hemoglobin . Nature Genetics . 42 . 9 . 801–5 . September 2010 . 20676099 . 2930131 . 10.1038/ng.630 .
  11. Book: Daniels . Geoff . Human blood groups . 15 April 2013 . John Wiley & Sons . 978-1-4443-3324-4 . 267–270 . 3rd.

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