The invention provides an agent that reduces the expression of Gα12 or Gα13 polypeptide, as well as an agent that enhances G protein Gα12 or Gα13 expression and/or activity. An agent of the invention may be used to decrease or increase G protein Gα12 or Gα13 expression and/or activity thereby to treat or prevent the onset of a disease or condition associated with Gα12 or Gα13 expression and/or activity. The invention also provides a method for screening for an anti-cancer or anti-angiogenesis agent, as well as an agent that promotes angiogenesis.
