Songbin Fu

The Genetic Legacy of the Mongols

We have identified a Y-chromosomal lineage with several unusual features. It was found in 16 populations throughout a large region of Asia, stretching from the Pacific to the Caspian Sea, and was present at high frequency: approximately 8% of the men in this region carry it, and it thus makes up approximately 0.5% of the world total. The pattern of variation within the lineage suggested that it originated in Mongolia approximately 1,000 years ago. Such a rapid spread cannot have occurred by chance; it must have been a result of selection. The lineage is carried by likely male-line descendants of Genghis Khan, and we therefore propose that it has spread by a novel form of social selection resulting from their behavior.

Male Demography in East Asia: A North–South Contrast in Human Population Expansion Times

The human population has increased greatly in size in the last 100,000 years, but the initial stimuli to growth, the times when expansion started, and their variation between different parts of the world are poorly understood. We have investigated male demography in East Asia, applying a Bayesian full-likelihood analysis to data from 988 men representing 27 populations from China, Mongolia, Korea, and Japan typed with 45 binary and 16 STR markers from the Y chromosome. According to our analysis, the northern populations examined all started to expand in number between 34 (18–68) and 22 (12–39) thousand years ago (KYA), before the last glacial maximum at 21–18 KYA, while the southern populations all started to expand between 18 (6–47) and 12 (1–45) KYA, but then grew faster. We suggest that the northern populations expanded earlier because they could exploit the abundant megafauna of the “Mammoth Steppe,” while the southern populations could increase in number only when a warmer and more stable climate led to more plentiful plant resources such as tubers.

A novel toll-like receptor that recognizes vesicular stomatitis virus

Toll-like receptors (TLRs) are the key molecular sensors used by the mammalian innate immune system to detect various types of pathogens. Tlr13 is a novel and uncharacterized member of the mammalian TLR family. Here we report the cloning and characterization of tlr13. Tlr13 is predominantly expressed in the spleen, particularly in dendritic cells and macrophages. Tlr13 appears to activate a MyD88- and TAK1-dependent TLR signaling pathway, inducing the activation of NF-κB. This receptor can also activate type 1 interferon through IRF7. Furthermore, Tlr13 seems to be another intracellular TLR. Remarkably, cells expressing tlr13 fail to respond to known TLR ligands but instead respond specifically to vesicular stomatitis virus. Cells with the knockdown of tlr13 are highly susceptible to vesicular stomatitis virus infection. Thus, these results provide an important insight into the potential role of the novel Toll-like receptor tlr13 in the recognition of viral infection.

Lysine 63-linked Polyubiquitination of TAK1 at Lysine 158 Is Required for Tumor Necrosis Factor α- and Interleukin-1β-induced IKK/NF-κB and JNK/AP-1 Activation

Transforming growth factor-β-activated kinase 1 (TAK1) plays an essential role in the tumor necrosis factor α (TNFα)- and interleukin-1β (IL-1β)-induced IκB kinase (IKK)/nuclear factor-κB (NF-κB) and c-Jun N-terminal kinase (JNK)/activator protein 1 (AP-1) activation. Here we report that TNFα and IL-1β induce Lys63-linked TAK1 polyubiquitination at the Lys158 residue within the kinase domain. Tumor necrosis factor receptor-associated factors 2 and 6 (TRAF2 and -6) act as the ubiquitin E3 ligases to mediate Lys63-linked TAK1 polyubiquitination at the Lys158 residue in vivo and in vitro. Lys63-linked TAK1 polyubiquitination at the Lys158 residue is required for TAK1-mediated IKK complex recruitment. Reconstitution of TAK1-deficient mouse embryo fibroblast cells with TAK1 wild type or a TAK1 mutant containing a K158R mutation revealed the importance of this site in TNFα and IL-1β-mediated IKK/NF-κB and JNK/AP-1 activation as well as IL-6 gene expression. Our findings demonstrate that Lys63-linked polyubiquitination of TAK1 at Lys158 is essential for its own kinase activation and its ability to mediate its downstream signal transduction pathways in response to TNFα and IL-1β stimulation.

USP4 targets TAK1 to downregulate TNFα-induced NF-κB activation

Lys63-linked polyubiquitination of transforming growth factor-β-activated kinase 1 (TAK1) has an important role in tumor necrosis factor-α (TNFα)-induced NF-κB activation. Using a functional genomic approach, we have identified ubiquitin-specific peptidase 4 (USP4) as a deubiquitinase for TAK1. USP4 deubiquitinates TAK1 in vitro and in vivo. TNFα induces association of USP4 with TAK1 to deubiquitinate TAK1 and downregulate TAK1-mediated NF-κB activation. Overexpression of USP4 wild type, but not deuibiquitinase-deficient C311A mutant, inhibits both TNFα- and TAK1/TAB1 co-overexpression-induced TAK1 polyubiquitination and NF-κB activation. Notably, knockdown of USP4 in HeLa cells enhances TNFα-induced TAK1 polyubiquitination, IκB kinase phosphorylation, IκBα phosphorylation and ubiquitination, as well as NF-κB-dependent gene expression. Moreover, USP4 negatively regulates IL-1β-, LPS- and TGFβ-induced NF-κB activation. Together, our results demonstrate that USP4 serves as a critical control to downregulate TNFα-induced NF-κB activation through deubiquitinating TAK1.

Phosphorylation of Thr-178 and Thr-184 in the TAK1 T-loop Is Required for Interleukin (IL)-1-mediated Optimal NFκB and AP-1 Activation as Well as IL-6 Gene Expression

TAK1 (transforming growth factor-β-activated kinase 1), a mitogen-activated protein kinase kinase kinase, is activated by various cytokines, including interleukin-1 (IL-1). However, the precise regulation for TAK1 activation at the molecular level is still not fully understood. Here we report that dual phosphorylation of Thr-178 and Thr-184 residues within the kinase activation loop of TAK1 is essential for TAK1-mediated NFκB and AP-1 activation. Once co-overexpressed with TAB1, TAK1 mutant with alanine substitution of these two residues fails to activate IKKβ-mediated NFκB and JNK-mediated AP-1, whereas TAK1 mutant with replacement of these two sites with acidic residues acts like the TAK1 wild type. Consistently, TAK1 mutant with alanine substitution of these two residues severely inhibits IL-1-induced NFκB and AP-1 activities, whereas TAK1 mutant with replacement of these two sites with acidic residues slightly enhances IL-1-induced NFκB and AP-1 activities compared with the TAK1 wild-type. IL-1 induces the phosphorylation of endogenous TAK1 at Thr-178 and Thr-184. Reconstitution of TAK1-deficient mouse embryo fibroblast cells with wild-type TAK1 or a TAK1 mutant containing threonine 178 and 184 to alanine mutations revealed the importance of these two sites in IL-1-mediated IKK-NFκB and JNK-AP-1 activation as well as IL-1-induced IL-6 gene expression. Our finding is the first report that substitution of key serine/threonine residues with acidic residues mimics the phosphorylated state of TAK1 and renders TAK1 active during its induced activation.

PPM1A and PPM1B act as IKKβ phosphatases to terminate TNFα-induced IKKβ-NF-κB activation

IKKbeta serves as a central intermediate signaling molecule in the activation of the NF-kappaB pathway. However, the precise mechanism for the termination of IKKbeta activity is still not fully understood. Using a functional genomic approach, we have identified two protein serine/threonine phosphatases, PPM1A and PPM1B, as IKKbeta phosphatases. Overexpression of PPM1A or PPM1B results in dephosphorylation of IKKbeta at Ser177 and Ser181 and termination of IKKbeta-induced NF-kappaB activation. PPM1A and PPM1B associate with the phosphorylated form of IKKbeta, and the interaction between PPM1A/PPM1B and IKKbeta is induced by TNFalpha in a transient fashion in the cells. Furthermore, knockdown of PPM1A and PPM1B expression enhances TNFalpha-induced IKKbeta phosphorylation, NF-kappaB nuclear translocation and NF-kappaB-dependent gene expression. These data suggest that PPM1A and PPM1B play an important role in the termination of TNFalpha-mediated NF-kappaB activation through dephosphorylating and inactivating IKKbeta.

Recent Spread of a Y-Chromosomal Lineage in Northern China and Mongolia

We have identified a Y-chromosomal lineage that is unusually frequent in northeastern China and Mongolia, in which a haplotype cluster defined by 15 Y short tandem repeats was carried by approximately 3.3% of the males sampled from East Asia. The most recent common ancestor of this lineage lived 590 +/- 340 years ago (mean +/- SD), and it was detected in Mongolians and six Chinese minority populations. We suggest that the lineage was spread by Qing Dynasty (1644-1912) nobility, who were a privileged elite sharing patrilineal descent from Giocangga (died 1582), the grandfather of Manchu leader Nurhaci, and whose documented members formed approximately 0.4% of the minority population by the end of the dynasty.

USP11 negatively regulates TNFα-induced NF-κB activation by targeting on IκBα

IkappaBalpha serves as a central anchoring molecule in the sequestration of NF-kappaB transcription factor in the cytoplasm. Ubiquitination-mediated IkappaBalpha degradation immediately precedes and is required for NF-kappaB nuclear translocation and activation. However, the precise mechanism for the deubiquitination of IkappaBalpha is still not fully understood. Using a proteomic approach, we have identified Ubiquitin Specific Peptidase 11 (USP11) as an IkappaBalpha associated deubiquitinase. Overexpression of USP11 inhibits IkappaBalpha ubiquitination. Recombinant USP11 catalyzes deubiquitination of IkappaBalpha in vitro. Moreover, knockdown of USP11 expression enhances TNFalpha-induced IkappaBalpha ubiquitination and NF-kappaB activation. These data demonstrate that USP11 plays an important role in the downregulation of TNFalpha-mediated NF-kappaB activation through modulating IkappaBalpha stability. In addition, overexpression of a catalytically inactive USP11 mutant partially inhibits TNFalpha- and IKKbeta-induced NF-kappaB activation, suggesting that USP11 also exerts a non-catalytic function in its negative regulation of TNFalpha-mediated NF-kappaB activation. Thus, IkappaBalpha ubiquitination and deubiquitination processes function as a Yin-Yang regulatory mechanism on TNFalpha-induced NF-kappaB activation.

Involvement of Annexin A2 in p53 induced apoptosis in lung cancer

Tumor suppressor p53 plays important roles in cell cycle regulation, apoptosis and DNA repair in different cell types including lung cancer. There are different p53 apoptotic pathways in high and low metastatic ability lung cancer cells. However, the exactly mechanism in the pathway is still unclear. Here we found that Annexin A2, a Ca2+-dependent phospholipid-binding protein, is involved in p53-mediated apoptosis. First, by using mRNA differential display technique, down-regulated Annexin A2 expression was found in all cell lines transfected of Ad-p53 (adenoviral expression construct encoding wild type p53 gene) especially in highly metastatic Anip973 lung cancer cells. Then, decreased expression of Annexin A2 was further confirmed by Northern blot and Western blot analysis. At last, knock down of Annexin A2 by siRNA inhibited cellular proliferation in BE1 cell line with highly metastatic ability. Taken together, our results suggested that Annexin A2 may play roles in p53 induced apoptosis and it is also involved in regulation of cell proliferation.