Corrigendum: Expression of constitutive fusion of ubiquitin to PCNA restores the level of immunoglobulin A/T mutations during somatic hypermutation in the Ramos cell line.

[This corrects the article DOI: 10.3389/fimmu.2022.871766.].

Multimodal cartography of human lymphopoiesis reveals B and T/NK/ILC lineages are subjected to differential regulation.

The developmental cartography of human lymphopoiesis remains incompletely understood. Here, we establish a multimodal map demonstrating that lymphoid specification follows independent direct or stepwise hierarchic routes converging toward the emergence of newly characterized CD117lo multi-lymphoid progenitors (MLPs) that undergo a proliferation arrest before entering the CD127- (NK/ILC/T) or CD127+ (B) lymphoid pathways. While the differentiation of CD127- early lymphoid progenitors is mainly driven by Flt3 signaling, emergence of their CD127+ counterparts is regulated cell-intrinsically and depends exclusively on the divisional history of their upstream precursors, including hematopoietic stem cells. Further, transcriptional mapping of differentiation trajectories reveals that whereas myeloid granulomonocytic lineages follow continuous differentiation pathways, lymphoid trajectories are intrinsically discontinuous and characterized by sequential waves of cell proliferation allowing pre-commitment amplification of lymphoid progenitor pools. Besides identifying new lymphoid specification pathways and regulatory checkpoints, our results demonstrate that NK/ILC/T and B lineages are under fundamentally distinct modes of regulation. (149 words).

Distinct subsets of multi-lymphoid progenitors support ontogeny-related changes in human lymphopoiesis.

Changes in lymphocyte production patterns occurring across human ontogeny remain poorly defined. In this study, we demonstrate that human lymphopoiesis is supported by three waves of embryonic, fetal, and postnatal multi-lymphoid progenitors (MLPs) differing in CD7 and CD10 expression and their output of CD127-/+ early lymphoid progenitors (ELPs). In addition, our results reveal that, like the fetal-to-adult switch in erythropoiesis, transition to postnatal life coincides with a shift from multilineage to B lineage-biased lymphopoiesis and an increase in production of CD127+ ELPs, which persists until puberty. A further developmental transition is observed in elderly individuals whereby B cell differentiation bypasses the CD127+ compartment and branches directly from CD10+ MLPs. Functional analyses indicate that these changes are determined at the level of hematopoietic stem cells. These findings provide insights for understanding identity and function of human MLPs and the establishment and maintenance of adaptative immunity.

Expression of Constitutive Fusion of Ubiquitin to PCNA Restores the Level of Immunoglobulin A/T Mutations During Somatic Hypermutation in the Ramos Cell Line.

Somatic hypermutation (SHM) of immunoglobulin (Ig) genes is a B cell specific process required for the generation of specific and high affinity antibodies during the maturation of the immune response against foreign antigens. This process depends on the activity of both activation-induced cytidine deaminase (AID) and several DNA repair factors. AID-dependent SHM creates the full spectrum of mutations in Ig variable (V) regions equally distributed at G/C and A/T bases. In most mammalian cells, deamination of deoxycytidine into uracil during S phase induces targeted G/C mutagenesis using either direct replication of uracils or TLS mediated bypass, however only the machinery of activated B lymphocytes can generate A/T mutagenesis around AID-created uracils. The molecular mechanism behind the latter remains incompletely understood to date. However, the lack of a cellular model that reproduces both G/C and A/T mutation spectra constitutes the major hurdle to elucidating it. The few available B cell lines used thus far to study Ig SHM indeed undergo mainly G/C mutations, that make them inappropriate or of limited use. In this report, we show that in the Ramos cell line that undergoes constitutive G/C-biased SHM in culture, the low rate of A/T mutations is due to an imbalance in the ubiquitination/deubiquitination reaction of PCNA, with the deubiquitination reaction being predominant. The inhibition of the deubiquitinase complex USP1-UAF1 or the expression of constitutive fusion of ubiquitin to PCNA provides the missing clue required for DNA polymerase η recruitment and thereafter the introduction of A/T base pair (bp) mutations during the process of IgV gene diversification. This study reports the establishment of the first modified human B cell line that recapitulates the mechanism of SHM of Ig genes in vitro.

Pigmentation abnormalities in nucleotide excision repair disorders: Evidence and hypotheses.

Skin pigmentation abnormalities are manifested in several disorders associated with deficient DNA repair mechanisms such as nucleotide excision repair (NER) and double-strand break (DSB) diseases, a topic that has not received much attention up to now. Hereditary disorders associated with defective DNA repair are valuable models for understanding mechanisms that lead to hypo- and hyperpigmentation. Owing to the UV-associated nature of abnormal pigmentary manifestations, the outcome of the activated DNA damage response (DDR) network could be the effector signal for alterations in pigmentation, ultimately manifesting as pigmentary abnormalities in repair-deficient disorders. In this review, the role of the DDR network in the manifestation of pigmentary abnormalities in NER and DSB disorders is discussed with a special emphasis on NER disorders.

Energy Metabolism Rewiring Precedes UVB-Induced Primary Skin Tumor Formation.

Although growing evidence indicates that bioenergetic metabolism plays an important role in the progression of tumorigenesis, little information is available on the contribution of reprogramming of energy metabolism in cancer initiation. By applying a quantitative proteomic approach and targeted metabolomics, we find that specific metabolic modifications precede primary skin tumor formation. Using a multistage model of ultraviolet B (UVB) radiation-induced skin cancer, we show that glycolysis, tricarboxylic acid (TCA) cycle, and fatty acid ß-oxidation are decreased at a very early stage of photocarcinogenesis, while the distal part of the electron transport chain (ETC) is upregulated. Reductive glutamine metabolism and the activity of dihydroorotate dehydrogenase (DHODH) are both necessary for maintaining high ETC. Mice with decreased DHODH activity or impaired ETC failed to develop pre-malignant and malignant lesions. DHODH activity represents a major link between DNA repair efficiency and bioenergetic patterning during skin carcinogenesis.

Energy metabolism in skin cancers: A therapeutic perspective.

Skin cancers are the most common cancers worldwide. The incidence of common skin cancers, including basal cell carcinomas (BCCs), squamous cell carcinomas (SCCs) and melanomas, continues to rise by 5 to 7% per year, mainly due to ultraviolet (UV) exposure and partly because of aging. This suggests an urgent necessity to improve the level of prevention and protection for skin cancers as well as developing new prognostic and diagnostic markers of skin cancers. Moreover, despite innovative therapies especially in the fields of melanoma and carcinomas, new therapeutic options are needed to bypass resistance to targeted therapies or treatment's side effects. Since reprogramming of cellular metabolism is now considered as a hallmark of cancer, some of the recent findings on the role of energy metabolism in skin cancer initiation and progression as well as its effect on the response to targeted therapies are discussed in this review. This article is part of a Special Issue entitled Mitochondria in cancer, edited by Giuseppe Gasparre, Rodrigue Rossignol and Pierre Sonveaux.

NADPH Oxidase-1 Plays a Key Role in Keratinocyte Responses to UV Radiation and UVB-Induced Skin Carcinogenesis.

The nicotinamide adenine dinucleotide phosphate oxidase (NOX) family enzymes are involved in several physiological functions. However, their roles in keratinocyte responses to UV radiation have not been clearly elucidated. This study shows that, among other NOX family members, UVB irradiation results in a biphasic activation of NOX1 that plays a critical role in defining keratinocyte fate through the modulation of the DNA damage response network. Indeed, suppression of both bursts of UVB-induced NOX1 activation by using a specific peptide inhibitor of NOX1 (InhNOX1) is associated with increased nucleotide excision repair efficiency and reduction of apoptosis, which is finally translated into decreased photocarcinogenesis. On the contrary, when only the second peak of UVB-induced NOX1 activation is blocked, both nucleotide excision repair efficiency and apoptosis are decreased. Our results show that inhibition of NOX1 activation could be a promising target for the prevention and treatment of UVB-induced skin cancer in nucleotide excision repair-proficient and -deficient patients.

Polymorphisms of RPS6KB1 and CD86 associates with susceptibility to multiple sclerosis in Iranian population.

OBJECTIVE:  Multiple sclerosis (MS) is the most prevalent disorder of nervous system inflammation which involves demyelination of spinal cord; this process depends on both environmental and genetic susceptibility factors. In the present study, we examined the association between two SNPs in RPS6KB1 (rs180515) and CD86 (rs9282641) with MS in Iranian population. RPS6KB1gene encodes p70S6K1 protein which plays a key role in mTOR signaling pathway, while CD86 gene codes a membrane protein type I which belongs to immunoglobulin super family act on co-stimulation signaling pathway. METHODS: In this case-control study 130 patients with MS and 128 matched healthy controls were enrolled, genomic DNA was isolated and genotyping was performed using mismatched PCR-RFLP. The results were finally analyzed using SPSS. RESULTS: Our results showed significant difference in allelic frequency of SNP rs180515 among cases and controls (P = 0.004). For this variation, AA genotype was shown to have protective effect (P = 0.016 and OR = 0.6), while GG genotype was a susceptive genotype to MS (P = 0.04 and OR = 2.2). Allelic frequency of SNP rs9282641 also showed significant difference between cases and controls (P = 0.006). For this SNP, AG genotype had predisposing effect (P = 0.04, OR = 2.3), and GG genotype showed protective (P = 0.01, OR = 0.411). CONCLUSION: We successfully replicated the association of two novel SNPs introduced by a GWAS study, and MS in the Iranian population. This result can open ways for better understanding the mechanisms involved in MS.