Human splicing factors Hprp3p and Hprp4p are associated with the U4/U6 small nuclear ribonucleoprotein particle, which is essential for the assembly of an active spliceosome. Currently, little is known about the specific roles of these factors in splicing. In this study, we characterized the molecular interaction between Hprp3p and Hprp4p. Constructs were created for expression of Hprp3p or its mutants in bacterial or mammalian cells. We showed that antibodies against either Hprp3p or Hprp4p were able to pull-down the Hprp3p-Hprp4p complex formed in Escherichia coli lysates. By co-immunoprecipitation and isothermal titration calorimetry, we demonstrated that purified Hprp3p and its mutants containing the central region, but lacking either the N-terminal 194 amino acids or the C-terminal 240 amino acids, were able to interact with Hprp4p. Conversely, Hprp3p mutants containing only the N-or Cterminal region did not interact with Hprp4p. In addition, by co-immunoprecipitation, we showed that intact Hprp3p and its mutants containing the central region interacted with Hprp4p in HeLa cell nuclear extracts. Primer extension analysis illustrated that the central region of Hprp3p is required to maintain the association of Hprp3p-Hprp4p with U4/U6 small nuclear RNAs, suggesting that this Hprp3p/Hprp4p interaction allows the recruitment of Hprp4p, and perhaps other protein(s), to the U4/U6 small nuclear ribonucleoprotein particle.Pre-mRNA splicing occurs in the spliceosome, a large RNAprotein complex that contains a pre-mRNA, four essential small nuclear ribonucleoprotein (snRNP) 1 particles (U1, U2, U5, and U4/U6), and numerous non-snRNP splicing factors (1-3). Each snRNP particle consists of one (U1, U2, and U5) or two (U4/U6) snRNAs complexed with a set of Sm or Sm-like proteins and several particle-specific proteins (4 -6). These snRNPs recognize conserved sequences of the pre-mRNA and assemble into a catalytically active spliceosome that catalyzes the two cleavage-ligation reactions of pre-mRNA splicing (1,2,7,8). Spliceosome assembly follows an ordered pathway through the formation of several intermediate complexes (2). First, a pre-spliceosome (A complex) is formed once U1 and U2 snRNAs (as part of the U1 and U2 snRNPs) associate with the conserved 5Ј-splice site and the branch point of the intron, respectively (9, 10). Then, U4/U6 snRNP, in which U4 and U6 snRNAs base pair over an extended complementary region, forming a Y-shaped junction, is recruited together with U5 snRNP, presumably via protein/protein interactions, to the pre-spliceosome to form the mature spliceosome (B complex) (11-13).Prior to the first catalytic step of splicing, important conformational rearrangements occur to create a catalytically active spliceosome. For example, U1 snRNA dissociates from the 5Ј-splice site, and the U4/U6 snRNA association is disrupted (14 -16), leaving the U6 snRNA free to base pair with both the U2 snRNA and the 5Ј-splice site (17). The U2 and U6 snRNAs, together with the pre-mRNA, may form the catalytic core of the s...

Chicken ovalbumin upstream promoter-transcription factor II (COUP-TFII) plays an essential role in angiogenesis and development. It is differentially expressed in tumor cell lines, but its role in carcinogenesis is largely unknown. We demonstrate here that noninvasive human lung cancer cells become invasive when COUP-TFII was expressed. The expression of extracellular matrix degrading proteinases, such as matrix metalloproteinase 2 and urokinase-type plasminogen activator, was upregulated in these cells. This finding was confirmed by transduction of different human lung cancer cell lines with COUP-TFII protein and also by using antisense expression. We observed disorganization of actin filaments and focal adhesion kinase phosphorylation in COUP-TFII-transfected human lung cancer cells in addition to the increase in extracellular metalloproteinase activity. These results suggest that COUP-TFII may be considered as a new target for anticancer therapies.