Infantile Myelofibrosis and Myeloproliferation with CDC42 Dysfunction

Abstract

Studies of genetic blood disorders have advanced our understanding of the intrinsic regulation of hematopoiesis. However, such genetic studies have only yielded limited insights into how interactions between hematopoietic cells and their microenvironment are regulated. Here, we describe two affected siblings with infantile myelofibrosis and myeloproliferation that share a common de novo mutation in the Rho GTPase CDC42 (Chr1:22417990:C>T, p.R186C) due to paternal germline mosaicism. Functional studies using human cells and flies demonstrate that this CDC42 mutant has altered activity and thereby disrupts interactions between hematopoietic progenitors and key tissue microenvironmental factors. These findings suggest that further investigation of this and other related disorders may provide insights into how hematopoietic cell-microenvironment interactions play a role in human health and can be disrupted in disease. In addition, we suggest that deregulation of CDC42 may underlie more common blood disorders, such as primary myelofibrosis.

The Ever-Increasing Array of Novel Inborn Errors of Immunity: an Interim Update by the IUIS Committee

“… Abbreviations : AR , autosomal recessive; AD , autosomal dominant; AID , activation-induced cytidine deaminase; CSR , class switch recombination; SHM , somatic hypermutation; MDS , myelodysplastic syndrome; LOE , loss of expression; LOF , loss of function; GOF , gain of function; DN , dominant negative; MSMD , Mendelian susceptibility to mycobacterial disease; HLH , hemophagocytic lymphohistiocytosis; FTT , failure to thrive; hPSC , human pluripotent stem cells; iPSC , induced pluripotent stem cells; CMV , cytomegalovirus • Not all Tables in the 2020 classifications [ 2 , 3 ] are listed in the “Table” column because not all Tables are represented by the new variants detailed above • Mutations in PAX1 previously reported to cause OTFCS2 (but CID/SCID not reported) [ 49 ] • Variants in IL6ST have been previously listed to cause an IEI due to recessive partial LOF alleles [ 50 ] • Dominant-negative mutations in IL6ST all target the intracellular domain of gp130, truncating the STAT3 binding sites as well as recycling motif, leading to sustained expression of a dead receptor (as opposed to recessive alleles, when detected in heterozygous carriers are benign) • Fnip1 ko mice also previously reported [ 12 , 13 ]; humans very similar • Variants in CEBPE have been previously listed to cause an IEI due to recessive LOF alleles [ 51 ] • Mutations in CDC42 previously identified in individuals with neurodevelopmental delay (Takenouchi-Kosaki syndrome) [ 52 ]; in these patients with autoinflammation and CDC42 mutations no such features were noted, except mild facial dysmorphism in some [ 33 – 39 ] .• Variants in STAT2 have been previously listed to cause an IEI due to recessive LOF alleles [ 53 , 54 ] • The same amino acid was found to be affected (R148Q/W) for both families affected by STAT2 GOF [ 53 , 54 ] • Variants in RIPK1 have been previously listed to cause an IEI due to recessive LOF alleles [ 55 , 56 ]; the heterozygous dominant mutations in RIPK1 reported here all affect the D324 amino acid residue that is important for cleavage …”

“…• ↑ serum levels of IL1, IL18, IFN-γ, ferritin, sCD25, CRP etc. • Recurrent GIT/RT infection; • Neurodevelopmental delay, FTT • Mutation affects actin function; • Treated with Anakinra/ IFN-γ mAb ↓NK function (cytox), Table 7 Subtable 1 [ 33 – 39 ] STAT2 (GOF, 3 patients; all deceased; 2 additional deceased sibs but not genotyped; 2 unrelated families) AR (GOF) • Low frequency of NK, ↑ frequency of T cells (esp naïve), normal NK degranulation • Total B cell frequencies within age-matched controls’ ranges • slight ↑ transitional and naïve B cells %‘s • Low/normal • Severe fatal early-onset autoinflammation (skin ulceration, fever, seizures, intracranial calcification, multiorgan dysfunction, abnormal neurodevelopment; phenocopy of USP18 deficiency) • ↑ serum IFN-α, IL6, TNFα • IFN-opathy gene signature (impaired regulation of late cellular responses to type 1 IFN), Validation • Study of the mutant STAT2 alleles in STAT2 deficient human cell line, and patient’s immortalized fibroblasts • Patient cells hyper-sensitive to IFN-α → prolonged JAK/STAT signaling/transcriptional activation • Biochemical confirmation that mutant allele is GOF in homozygous, but not heterozygous, combination • Impaired interaction of GOF STAT2 protein with USP18, a negative regulator of type 1 IFN responses Table 7 Subtable 1 [ 40 , 41 ] RIPK1 (12 patients; 5 families, 2 papers) AD • Normal T and NK cell numbers • Low/normal CD4 + T cells • Normal/hi CD8 + T cells • ↑ DN T cells • Normal B cells ND • Autoinflamm disorder: regular/prolonged fevers, lymphadenopathy, spleno/hepatomegaly, ulcers, arthralgia, GI features, • ↑ inflamm markers, ↑ pro-inflamm cytokines/gene signature; • Responsive to Tocilizumab (not IL1/TNF blockade) Table 7 Subtable 2 [ 42 , 43 ] NCKAP1L (9 patients; 7 families, 3 papers) AR (LOF) • Normal T cell numbers • ↑T CM , exhausted cells; • Possibly immature NK cells but intact function • Normal B cells and naïve/memory subsets • ↑ CD21 lo cells • Normal/ ↑ Ig levels • autoAbs • Recurrent URTI, skin rashes/abscesses, ulcers, • Anti dsDNA Abs, SLE-like, lymphadenopathy, fever, HLH-like • FTT • Immunodeficiency coupled with atopy, lymphoproliferation, hyperinflammation ,and cytokine overproduction (↑ Th1)...…”

“…• Mutations in CDC42 previously identified in individuals with neurodevelopmental delay (Takenouchi-Kosaki syndrome) [ 52 ]; in these patients with autoinflammation and CDC42 mutations no such features were noted, except mild facial dysmorphism in some [ 33 – 39 ]…”

Une palmitoylation de CDC42 causée par une mutation déclenche un syndrome auto-inflammatoire sévère

“…Sur le plan fonctionnel, la mutation Arg-186Cys de CDC42 entraîne une diminution de la polymérisation des filaments d'actine dans les fibroblastes primaires du patient et dans une lignée lymphoblastique T [5] (Figure 2). Cette observation a été confirmée par d'autres équipes, qui ont également observé une altération de l'organisation du cytosquelette, de la morphologie cellulaire, de la prolifération et de la migration cellulaires [7,9]. La perturbation, par la mutation, de la liaison de CDC42 avec les effecteurs WASP et IQGAP (IQ motifcontaining GAP) pourrait expliquer ces effets [5,7].…”

“…Récemment, nous avons identifié une nouvelle mutation, Arg186Cys, chez un patient atteint d'un syndrome autoinflammatoire sévère [5] (Figure 1). La même mutation a également été identifiée chez plusieurs autres patients présentant des phénotypes hématologiques, immunitaires et auto-inflammatoires similaires [5][6][7][8][9].…”