The attorney general and reporter shall attend in person, or by assistant, and prosecute or defend, as the case may be, any and all suits, civil or criminal, in the supreme court of the United States, in the United States court of appeals for the judicial circuit of the United States comprising the state of Tennessee, or in any of the district courts of the United States held in the state of Tennessee, in which suit or suits the state may be a party, or in which the state has or may have interests of a pecuniary nature.